Hastings' Dictionary of the New Testament 
Reserve —In Matthew 7:6 Jesus counsels reserve in the communication of religious truth. That maxim, which has had great and sinister developments in the Church, stands alone, both in its place in the Sermon on the Mount and in His teaching. Its meaning, then, can be gathered only from His practice.
1. It was never Jesus’ custom to meet religious curiosity or speculation . As He was teaching, one said unto Him, ‘Lord, are there few that be saved!’ ( Luke 13:22-25). He did not answer; He said, ‘Strive to enter in at the strait gate …’ He turned His hearers’ attention from that speculation, which has no saving power in it, to the clear duty and wisdom of the moment. When Peter asked if the parable of the Servants waiting for their Lord was addressed to the disciples specially, or to all, Jesus did not answer ( Luke 12:41). He painted, instead, another picture for the inward eye of the heart. In both cases it was the practical and most imperative needs of the soul’s relation to God that He considered. That directing purpose shown in these cases, explains the silences of His teaching, the reserves of His revelation. When He spoke of those on whom the tower fell, and of the Galilaeans whose blood Pilate had mingled with their sacrifices ( Luke 13:1-5), the old problem of the suffering of the innocent was suggested; but He shed no light upon it. He made practical use of it, instead, as a call to repentance. The immortality of the soul is the presupposition of all His teaching about the love of the Heavenly Father for men, His children. ‘The life after death, Lightfoot and I agreed, is the cardinal point of Christianity’ ( In Memoriam , Author’s Notes, p. 227 n. [Note: note.] ). But Jesus, of His own impulse, only enunciates this truth at the end of His mission. And a practical need then impelled Him. His disciples needed consolation for the days after His death, and He left them the hope which would strengthen their faith and loyalty (John 14). With Jesus, the declaration of any truth depended wholly upon the needs of faith in the heart.
2. Jesus practised reserve as to His personal claims . The Jews came and asked Him, ‘How long dost thou make us doubt: if thou be the Christ, tell us plainly’ ( John 10:24). They were surprised at His silence about what seemed to them so important. And His blessing of Peter ( Matthew 16:13-17) shows that He had been silent also in private, even among the inner circle of His disciples. His reserve is explained, not by the slow growth of His own conception of His Messiahship, but by the method of establishing the Kingdom of God which He had set before Him from the beginning. The weapons of His warfare were to be purely spiritual. His aim was to set up the Kingdom within men’s hearts, to win their heart’s love and trust in the Father. And for that end the appeal of all His activities, miracles of help and healing and words of teaching, was single. He aimed at the heart, the seat and source of faith, where the vision and the love of goodness, with their dynamic impulse, are. And Peter’s confession was a joy to Him, because it came from his heart’s assurance that Jesus had the words of eternal life ( John 6:68, Matthew 16:17). It was faith in goodness asserting itself against the appearance of things. To this faith Jesus confessed His greatness and Divine mission. He did so, because then He was merely certifying the Divine supremacy of that goodness which had, in its lowliness and simplicity, won the love and trust of their hearts. Through their faith they reached His authority. Jesus recognized no other path to faith in Him as Messiah, the revealer of the Father, and the founder of the Kingdom of God upon the earth. He sent the inquiring Jews back to this road ( John 10:25-27); He withdrew from the people who, from material ideas and expectations, would have made Him king ( John 6:15); and He declined to answer the chief priests and elders, who came inquiring for His authority, because they were not simple-hearted or honest inquirers ( Matthew 21:23-27). This single regard for the interests of faith in the heart explains also His reserve with the messengers of John ( John 11:2-6). John belonged to the old economy ( John 11:11); his prophecy of the Messiah’s coming had been a prophecy of judgment ( John 3:12). The simple acknowledgment by Jesus that He was the Messiah could never have brought to him enlightenment and faith as to that Kingdom of heaven whose least disciple was greater than he. Its inevitable consequence would have been to confirm him in his old expectations of judgment; it would have appeared to him a call to wait in patience the good time of the Messiah, when He would play the stern part John had foretold. Therefore Jesus gave no direct answer to John’s question. He pointed rather to all the gracious activities which were partly the causes of John’s doubting impatience. These were the signs of that Kingdom of love which Jesus was establishing; and if John were ever to gain the higher and richer conceptions of God and of man manifested there, he must see the Messiah through these quiet and lowly activities of loving helpfulness, and believe in Him as Him that should come, because of them and not despite them.
3. The sufferings of the Messiah .—It was immediately upon Peter’s confession that Jesus began to teach the necessity of suffering and death for Himself ( Matthew 16:21, Mark 8:31). There are a precision and a fulness of detail in the account of this teaching, which are probably reflected back upon it from later experience. But the tragic note enters then and dominates the later teaching both in public and private. Its emergence at that time does not prove that Jesus entered then upon a new conception of His mission, taught by the progress of events. It is more probable that this tragic note was in His conception of the task of establishing the Kingdom from the beginning. His wilderness temptation argues that ( Matthew 4:8-9); it is implicit in His Beatitudes upon the meek and the persecuted, and in His teaching of the earthly rewards of hypocrisy ( Matthew 6:2; Matthew 6:5; Matthew 6:16); and the deeper spirit of the OT, with its history of religious growth through the sufferings of the saints and the long-suffering patience of Jehovah’s love, could not be veiled from the insight of His meditation thereon in the years of His preparation. The joy of the early days does not contradict this. It was the natural answer of the heart to those new thoughts of the love of the Father which Jesus preached. And in Jesus’ own thought this tragic element was not in contradiction with that instinctive, buoyant joy in His gospel, though then He had many things to say to them which they could not bear ( John 16:12). Peter’s confession brought the opportunity of revealing further the depths of the riches of the wisdom and love of God.
Reserve, as practised by Jesus, was never a politic means of leading men’s minds gradually to doctrines which might startle or offend them at first sight; it consisted only in seeking, with a single aim, the practical needs of faith in the heart—belief in that Divine Love whose outgoings are redemptive, and in whose fellowship and service stands eternal life.
Literature.—Ker, Sermons , Ist ser. xx.; ExpT [Note: xpT Expository Times.] iv.  446; Paget, Studies in the Chr. Character , xxii.; J. Smith, The Magnetism of Christ (1904), 269; B. Whitefoord in ExpT [Note: xpT Expository Times.] vi. (1895) 22.
Webster's Dictionary 
(1): ( n.) A tract of land reserved, or set apart, for a particular purpose; as, the Connecticut Reserve in Ohio, originally set apart for the school fund of Connecticut; the Clergy Reserves in Canada, for the support of the clergy.
(2): ( n.) Funds kept on hand to meet liabilities.
(3): ( n.) See Army organization, above.
(4): ( n.) Restraint of freedom in words or actions; backwardness; caution in personal behavior.
(5): ( v. t.) Hence, to keep in store for future or special use; to withhold from present use for another purpose or time; to keep; to retain.
(6): ( v. t.) To keep back; to retain; not to deliver, make over, or disclose.
(7): ( n.) In exhibitions, a distinction which indicates that the recipient will get a prize if another should be disqualified.
(8): ( n.) The amount of funds or assets necessary for a company to have at any given time to enable it, with interest and premiums paid as they shall accure, to meet all claims on the insurance then in force as they would mature according to the particular mortality table accepted. The reserve is always reckoned as a liability, and is calculated on net premiums. It is theoretically the difference between the present value of the total insurance and the present value of the future premiums on the insurance. The reserve, being an amount for which another company could, theoretically, afford to take over the insurance, is sometimes called the reinsurance fund or the self-insurance fund. For the first year upon any policy the net premium is called the initial reserve, and the balance left at the end of the year including interest is the terminal reserve. For subsequent years the initial reserve is the net premium, if any, plus the terminal reserve of the previous year. The portion of the reserve to be absorbed from the initial reserve in any year in payment of losses is sometimes called the insurance reserve, and the terminal reserve is then called the investment reserve.
(9): ( n.) Usually, the uninvested cash kept on hand for this purpose, called the real reserve. In Great Britain the ultimate real reserve is the gold kept on hand in the Bank of England, largely represented by the notes in hand in its own banking department; and any balance which a bank has with the Bank of England is a part of its reserve. In the United States the reserve of a national bank consists of the amount of lawful money it holds on hand against deposits, which is required by law to be not less than 15 per cent (U. S. Rev. Stat. secs. 5191, 5192), three fifths of which the banks not in a reserve city (which see) may keep deposited as balances in national banks that are in reserve cities (U. S. Rev. Stat. sec. 5192).
(10): ( n.) That part of the assets of a bank or other financial institution specially kept in cash in a more or less liquid form as a reasonable provision for meeting all demands which may be made upon it;
(11): ( v. t.) To make an exception of; to except.
(12): ( n.) A preparation used on an object being electroplated to fix the limits of the deposit.
(13): ( n.) A resist.
(14): ( n.) That which is excepted; exception.
(15): ( n.) The act of reserving, or keeping back; reservation.
(16): ( n.) That which is reserved, or kept back, as for future use.
(17): ( n.) A body of troops in the rear of an army drawn up for battle, reserved to support the other lines as occasion may require; a force or body of troops kept for an exigency.
King James Dictionary 
RESERVE, rezerv'. L. reservo re and servo, to keep.
1. To keep in store for future or other use to withhold from present use for another purpose. The farmer sells his corn, reserving only what is necessary for his family.
Hast thou seen the treasures of hail, which I have reserved against the day of trouble? Job 38 .
2. To keep to hold to retain.
Will he reserve his anger for ever? Jeremiah 3 .
3. To lay up and keep for a future time. 2 Peter 2 .
Reserve your kind looks and language for private hours.
RESERVE, n. rezerv'.
1. That which is kept for other or future use that which is retained from present use or disposal.
The virgins, besides the oil in their lamps, carried likewise a reserve in some other vessel for a continual supply.
2. Something in the mind withheld from disclosure.
However any one may concur in the general scheme, it is still with certain reserves and deviations.
3. Exception something withheld.
Is knowledge so despis'd? or envy, or what reserve forbids to taste?
4. Exception in favor.
Each has some darling lust, which pleads for a reserve.
5. Restraint of freedom in words or actions backwardness caution in personal behavior. Reserve may proceed from modesty, bashfulness, prudence, prudery or sullenness.
My soul surpris'd, and from her sex disjoin'd, left all reserve, and all the sex behind.
6. In law, reservation.
In reserve, in store in keeping for other or future use. He has large quantities of wheat in reserve. He has evidence or arguments in reserve.
Body of reserve, in military affairs, the third or last line of an army drawn up for battle, reserved to sustain the other lines as occasion may require a body of troops kept for an exigency.
Vine's Expository Dictionary of NT Words 
"to guard, keep, preserve, give heed to," is translated "to reserve," (a) with a happy issue, 1—Peter 1:4; (b) with a retributive issue, 2—Peter 2:4; 2:9 , AV (RV, "keep"); 2:17; 3:7; Jude 1:6 , AV (RV, "hath kept"); 1:13; (c) with the possibility either of deliverance or execution, Acts 25:21 , AV (RV, "kept"). See Keep.