Fausset's Bible Dictionary 
Geerim . 1 Chronicles 22:2, "the strangers," in Septuagint "proselytes, i.e. comers to Palestine, sojourners ( Exodus 12:48; Exodus 20:10; Exodus 22:21; Leviticus 19:33). In New Testament converts to Judaism, "comers to a new and God-loving polity" (Philo). Israel's religious attitude attracted neighbouring people from the first. The Shechemites are an instance, only that passion and interest were their motive (Genesis 34). Circumcision was required as the condition. At the Exodus "a mixed multitude went up with Israel" ( Exodus 12:38). "The stranger" was bound by the law of the Sabbath ( Exodus 20:10; Exodus 23:12; Deuteronomy 5:14) and the Passover when he was circumcised ( Exodus 12:19; Exodus 12:48), the feast of weeks ( Deuteronomy 16:11), tabernacles ( Deuteronomy 16:14), the day of atonement ( Leviticus 16:29), prohibited marriages ( Leviticus 18:26), and blood ( Leviticus 17:10), and Moloch worship ( Leviticus 20:2), and blasphemy ( Leviticus 24:16).
The city of refuge was open to him ( Numbers 35:15). Kind treatment in remembrance of Israel's own position as strangers formerly in Egypt ( Exodus 22:21; Exodus 23:9; Deuteronomy 10:18-19; Leviticus 19:33-34), justice ( Leviticus 24:22; Deuteronomy 1:16; Deuteronomy 24:17; Deuteronomy 24:19-21), share in gleanings and tithe of the third year ( Deuteronomy 14:29), were the stranger's right. But he could not hold land nor intermarry with Aaron's descendants ( Leviticus 19:10; Leviticus 21:14), he is presumed to be in a subject condition ( Deuteronomy 29:11); Hobab and the Kenites ( Numbers 10:29-32; Judges 1:16), Rahab of Jericho ( Joshua 6:25), and the Gibeonites as "hewers of wood and drawers of water" (Joshua 9), are instances of strangers joined to Israel. The strangers were assembled with Israel at the feast of tabernacles at the cnd of every seven years, to hear the law ( Deuteronomy 31:10-12; Joshua 8:34-35).
Under the kings strangers rose to influential positions: Doeg the Edomite ( 1 Samuel 21:7), Uriah the Hittite ( 2 Samuel 11:3), Araunah the Jebusite ( 2 Samuel 24:23), Zelek the Ammonite ( 2 Samuel 23:37), Ithmah the Moabite ( 1 Chronicles 11:46, the law in Deuteronomy 23:3 forbidding an Ammonite or Moabite to enter the congregation to the tenth generation does not forbid their settlement in Israel, the law must have been written in times long before David whose great grandmother was Ruth the Moabtress), Ittai the Gittite ( 2 Samuel 15:19), Shebna the secretary of state under Hezekiah ( 2 Kings 18:37; Isaiah 22:15), Ebedmelech the Ethiopian under Zedekiah ( Jeremiah 38:7), the Cherethites and Pelethites. (See Cherethites ; Pelethites Hezekiah's triumph over Sennacherib was followed by many bringing gifts: unto Jehovah to Jerusalem ( 2 Chronicles 32:23); this suggested the prophecy in Psalm 87 that Rahab (Egypt) and Babylon (Whose King Merodach Baladan Had Sent A Friendly Embassy To Hezekiah) , Philistia, Tyre, and Ethiopia should be spiritually born ( Psalms 51:5; Psalms 51:10; Psalms 22:31; Isaiah 66:8; John 3:3; John 3:5; both Old and New Testament teach the need of the new birth) in Jerusalem as proselytes.
Tyre's alliance with David was a prophetic earnest of its future union with the kingdom of God, of which the Syrophoenician woman was a firstfruit ( Mark 7:26), as Candace's eunuch the proselyte (Acts 8) was a pledge of Ethiopia's conversion. In times of judgment on Israel for apostasy the stranger became "the head" ( Deuteronomy 28:43-44); but under David and Solomon they were made to do bondservice, 70,000 bearers of burdens, 80,000 hewers, 3,600 overseers ( 1 Chronicles 22:2; 2 Chronicles 2:17-18). In Psalms 94:6, as the pagan do not make widow and strangers their chief object of attack, "the stranger" is probably the saint in relation to this world ( Psalms 39:12), and "the widow" is the widowed church awaiting Christ's glorious epiphany to avenge her on antichrist ( Luke 18:3-8).
All the prophets anticipate the future sharing of proselytes in the kingdom of God, and even in the Holy Land as "sojourners" ( Ezekiel 47:22; Isaiah 2:2; Isaiah 11:10; Isaiah 56:3-6; Micah 4:1), and meantime plead their cause ( Jeremiah 7:6; Ezekiel 22:7; Ezekiel 22:29; Zechariah 7:10; Malachi 3:5). After the return from Babylon many "had separated themselves from the people of the lands unto the law of God" with their families ( Nehemiah 10:28). Many, in Esther's time ( Esther 8:17), "of the people of the land became Jews, for the fear of the Jews fell upon them." In New Testament times these appear in the synagogues ( Acts 13:42-43; Acts 13:50; Acts 17:4; Acts 18:7), come up to the feasts at Jerusalem ( Acts 2:10). Roman centurions, a class promoted for military good conduct, were noble specimens of these proselytes ( Luke 7:5; Acts 10:2; Acts 10:7; Acts 10:30), and were most open to gospel truth.
But Jewish fanaticism sought proselytes also by force and fraud, as John Hyrcanus offered the Idumeans the alternative of death, exile, or circumcision (Josephus, Ant. xiii, 9, section 3). Casuistry released the proselyte from moral obligations admitted before; and superstition chained him anew, hand and foot, e.g. the Korban ( Matthew 15:4-6); and circumcision, canceling all previous relationships, admitted of incestuous marriages. Any good in paganism was lost, and all that was bad in traditional Judaism was acquired. Thus the proselyte became "twofold more the child of hell" than the scribes themselves ( Matthew 23:15). Considering that the end justified the means, the scribes "compassed sea and land to make one proselyte," yet, when made, the Jews despised the proselyte as a "leprosy cleaving (in perversion of Isaiah 14:1) to the house of Jacob"; "no wise man would trust a proselyte to the 24th generation" (Jalkuth, Ruth f. 163 a). They classed them into
(1) "Love proselytes," wishing to gain the beloved one.
(2) Man for woman or woman for man, where one embraced the married partner's Judaism.
(3) Esther proselytes, to escape danger ( Esther 8:17).
(4) King's table proselytes, seeking to gain court favor, as under Solomon.
(5) Lion proselytes, through dread of judgments: 2 Kings 17:26 (Gem. Hieros., Kiddush 65, section 6). Simon ben Gamaliel said: "when a pagan comes to enter the covenant we ought to stretch out, our hand to him and bring him under the wings of God" (Jost, Judenth. 1:447).
The distinction between "proselytes of the gate" (from Exodus 20:10, "the stranger that is within thy gates") and "proselytes of righteousness" was minutely drawn by the talmudic rabbis and Maimonides (Hilc. Mel. 1:6). The proselytes of the gate were not bound to circumcision, only to the seven precepts of Noah, namely, the six said to have been given to Adam:
(1) against idolatry,
(6) the precept of obedience to authorities, and
(7) that given to Noah against "flesh with the blood"; but he had not the full Israelite privileges, he must not study the law nor redeem his firstborn.
But all this is rabbinical systematizing theory; in fact, the New Testament only in a general way recognizes two degrees of converts to Judaism. The eunuch of Candace was a sample of the full convert, circumcised and baptized at his admission (Otho, Lex Rabb., Baptism, for which the rabbis quoted Exodus 19:10), followed by his presenting the corban offering of two turtle doves, as after a birth ( Leviticus 12:8). The presumed existence of this proselyte baptism for males and females throws light on John's baptism and the priests' question, "why baptizest thou then?" ( John 1:25) and John 3:5; John 3:10, the Lord's words to Nicodemus, "art thou a master (teacher) of Israel, and knowest not these things?" Nicodemus ought to have understood the deeper sense to which Christ applied the familiar phrase "new birth" in connection with "baptism" of proselytes.
However, there is no mention of baptism of proselytes in the Bible, the Apocrypha, Philo, Josephus, or the older targums. The centurion Cornelius was a proselyte of a less strict kind, which the rabbis would call a proselyte of the gate; otherwise a special revelation would not have been needed to warrant Peter's opening the gospel kingdom to him, as it had not been needed to open the gospel to Candace's eunuch (Acts 8; 10). "Proselyte" occurs in New Testament only Matthew 23:15; Acts 2:10; Acts 6:5; Acts 13:43. The common phrase is" devout men," "fearing" or "worshipping God" ( Acts 10:2; Acts 10:7; Acts 13:16; Acts 13:26; Acts 13:43; Acts 13:50; Acts 16:14; Acts 17:4; Acts 17:17; Acts 18:7; John 12:20). From them came the largest accession to the Christian church.
Holman Bible Dictionary 
Matthew 23:15 Matthew 23:5
Gentiles were impressed by three features of Judaism. First, the concept of one God who created, sustains, and rules all things was clearly superior to polytheistic views. Second, Judaism stressed a life-style of moral responsibility with its monotheism; and third, it was a religion of ancient and stable tradition in contrast to the faddish cults of the time.
Proselytes usually embraced Judaism gradually because much needed to be learned, such as the proper observance of the sabbath and the careful following of the dietary rules, before one could win acceptance into the Jewish community. Persons attracted to Judaism and keeping the sabbath and food laws were termed fearers or worshipers of God. These terms appear in the New Testament where Cornelius ( Acts 10:1-2 ), and Lydia ( Acts 16:14 ) are so described (see also John 12:20; Acts 17:4; Acts 18:4 ).
Many God fearers went on to become proselytes or fully accepted and integrated members of the Jewish community. This involved fulfilling the Jewish demands of circumcision (males) which related one to the covenant (see Galatians 5:3 ), baptism (males and females) which made one ritually clean, and an offering (males and females) in the Jerusalem Temple which atoned for sin.
Harold S. Songer
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
This word is employed in modern language to designate such individuals as have abandoned their faith and embraced another, and who, in general, devote all their energy to the expansion of their new creed. The endeavor to gain others to one's own convictions. either by licit or illicit means, is called proselytism. Biblical representatives of this unfair system are the Pharisees. to whom Christ said, "Woe unto you, scribes and Pharisees, hypocrites! for ye compass sea and land to make one proselyte; and when he is made, ye make him twofold more the child of hell than yourselves." Every religion that believes in itself must feel impelled to propagate its creed; the followers of a doctrine to whom it is indifferent whether the number of those who share it with them increases or decreases have no true faith. The Christians are especially active in winning converts to their religion, but this spirit is due entirely not to a selfish desire to enlarge their borders and increase their numbers, but to give to all the world the great truths to establish which Christ came into the world in the form of man and suffered death upon the cross. It is, moreover, because of the direct command given by the Saviour of mankind that Christians feel impelled to make converts of all non-believers. (See Christianity); (See Missions).
A very different thing it is, however, for anybody, or for bodies of men, to Force conversion upon their fellows. The Jews were the chosen people of God. They had a right to consider themselves the armor-bearers of divine truth, and if they felt impelled to carry "the law and the prophets" to the strangers ( גֵּרַים ), it was only a reasonable consequence of the divine revelation which they had enjoyed. But it was by the fair means employed that they could best indicate the moral sublimity of divine teachings over philosophic schemes and heathenish systems of religion. When, therefore, the Jews, after the establishment of Maccaboean rule, conpelled, under Hyrcanus, the Idumeans, and, under Aristobulus, the Iturians, no embrace the Jewish faith and to subject themselves to circumcision, there was an adoption of measures for which the Old-Test. dispensation furnished no warrant; and though it may be conceded that their object was probably to advance the interests of true religion, they yet, by the adoption of unauthorized measures, evinced an unrighteous zeal which must have been underlaid by a selfish purpose. Thus the Roman Catholics have constantly striven for the propagation of the Christian faith by measures wholly unwarranted and not in uniformity with the lofty state of its ethics.
The Jesuit Sambuga says, in defence of the Jesuitic proselytism: "The mania of proselytism in priests is no mania, but a holy zeal." The prince- cardinial von Hohenlohe approves of this defence in his Lichtblicke und E'rlebnlisse aus der Welt und desm Priester-leben (Ratisbon, 1836, 8vo), p. 39. But this defence is, after all, a simple Jesuitic sophism. The mania of proselytism is a mania, and because priests are subject to it, it does not become therefore a holy zeal; or else we must admit that anything done by avaricious and ambitious priests of all persuasions (Christians and pagans) was holy, or was the result of a holy zeal, and therefore not blameworthy, but, on the contrary, praiseworthy and commendable. When proselytes are gained in such a wily or violent manner as that resorted to by Jesuits; when the means employed are money and promotions on one side, threats and persecutions on the other, we perceive in it the evidence of a most, unholy zeal, against which the founder of Christianity pronounced his anathema in his condemnation of the priests of his time, the doctors of the law, and Pharisees. For this very reason Christ called them "children of hell." (See Romanism). It is a curious fact worth remembering that one of the main features of the times of the Messiah was to be, according to Jewish tradition, the utter abolition of proselytism, and the entire ceasing of all distinctions of an opprobrious nature among men. The evil repute into which the term Proselyte had fallen in the times of Christ also caused the early converts to Christianity to adopt the name of Neophytes ( Newly Planted ) instead. (See Neophyte). (J. H. W.)
The Nuttall Encyclopedia 
Converts from heathenism to Judaism, of which there were two classes: Proselytes of the Temple, those who accepted the ceremonial law and were admitted into the inner court of The temple; and Proselytes of the Gate, who accepted only the moral law, and were admitted only into the outer court. They were a numerous class after the Dispersion, and were reckoned at hundreds of thousands.