Baker's Evangelical Dictionary of Biblical Theology 
Watchfulness suggests a preparedness in order to avoid being taken unaware by an enemy ( Psalm 127 ). It involves fighting carelessness to reach a desired goal ( Proverbs 8:34; see Nehemiah 4:9; 7:3 ). In the New Testament three basic emphases are found: (1) be prepared for the Lord's return; (2) be on guard against temptation; and (3) struggle in prayer.
The Lord's Return . In the Synoptic Gospels Jesus exhorts the disciples to be prepared for the coming of the Son of Man ( Mark 13:33-37 ). He employs a variety of parables and illustrations to paint word portraits of watchfulness (see Matthew 24:32-51 ). The disciples are even to abstain from sleep because the coming of the Son of Man will be unexpected, like a thief in the night.
Watchfulness characterizes the attitudes of the disciples who await with hope the return of Jesus. Vigilant watchfulness demands alertness and detachment from earthly pleasures and activities (see Luke 21:34-36 ). The parable of the ten virgins emphasizes the imminence of the parousia ( Matthew 25:1-13 ).
The Pauline epistles echo a similar theme. Paul's eschatological anticipations reflect the vigilance of the Gospels (see 1 Thessalonians 5:1-7 ). Believers must resist evil so as not to be taken by surprise at the Lord's coming. Watchfulness implies sobriety, an avoidance of worldly excesses associated with darkness. Beyond that believers must wake from their sleep to prepare for the consummation of their salvation ( Romans 13:11-14 ).
Guard against Temptation . Vigilant watchfulness for the Lord's return enables the disciples to battle temptation. The Synoptic Gospels picture Jesus' struggle in Gethsemane as an adumbration of the Church's struggle at the end of time. Jesus serves as a model of how to stand against temptation ( Matthew 4:1-11 ). The petition in the Lord's Prayer to be able to stand against temptation points not only toward the eschatological future, but to the daily enablement needed by believers ( Matthew 6:9-13 ).
Both Paul and Peter issue the command to be watchful, to stand against the evil one (see Ephesians 6:10-17; 1 Peter 5:8 ). The church must watch unless savage wolves, influenced by the evil one, overtake the community and lead it astray.
Watch and Pray . The picture of Jesus' stand against the devil's temptation is all the more powerful because of the disciples' failure to do the same. They fail to hear and obey their master's warning to watch and pray so as not to fall into temptation ( Matthew 26:41 ).
Paul urges the church to pray with unfailing perseverance. The actions of watchfulness and prayer are indissolubly united. Prayer is an act of vigilance and vigilance a consequence of prayer ( Ephesians 6:18-19 ). Vigilant watchfulness is a manifestation of genuine spiritual life. It keeps the church faithful in avoiding being lulled into false security.
David S. Dockery
Charles Buck Theological Dictionary 
Vigilance, or care to avoid surrounding enemies and dangers. We are to watch against the insinuations of Satan; the allurements of the world; the deceitfulness of our hearts; the doctrines of the erroneous; and, indeed, against every thing that would prove inimical to our best interests. We are to exercise this duty at all times, in all places, and under all circumstances, 1 Corinthians 16:13 . Luke 12:37 .
To watch, is also to wait for and expect: thus we are,
1. To watch the providence of God.
2. The fulfillment of the prophecies.
3. God's time for our deliverance from troubles, Psalms 130:1-8 :
4. We are to watch unto prayer, Ephesians 6:18 .
5. For death and judgment, Mark 13:37 .
Charles Spurgeon's Illustration Collection 
While the Austrian general was staying at the Hotel de Ville, upon the Grand Canal, at Venice, we lodged at the same house, and so often as we passed his rooms, whether by day or night, we encountered two sentries on guard at the door. Our heart said to itself; whenever the King of kings deigns to make a chamber of our spirit, let us set holiness and devotion to be sentries at the entrance. When our Beloved visits us he must not be disturbed; ill thoughts must be repulsed, and carnal desires kept at a distance. With drawn swords let watchfulness preserve the sanctity of Immanuel's rest. 'I charge you, O ye daughters of Jerusalem, by the roes and by the hinds of the field, that ye stir not up, nor awake my love, till he please.'