Revelation 3:2

be watchful
A present tense imperative participle (γίνου γρηγρῶν [ginou grēgrōn] ) : “you be continually watching!” The command to the church at Sardis is the same found throughout Scripture to all believers. They are to be continuously watching. “It is not merely the call to be awake; it is to remain awake, to keep a vigil as a watchman in the midst of a sleeping encampment.”1 The Sardian church was to be watchful because of the weakness of the flesh. “ ‘Watch and pray, lest you enter into temptation. The spirit indeed is willing, but the flesh is weak’ ” (Mtt. Mat. 26:41). They were to watch themselves:

But take heed to yourselves, lest your hearts be weighed down with carousing, drunkenness, and cares of this life, and that Day come on you unexpectedly. For it will come as a snare on all those who dwell on the face of the whole earth. Watch therefore, and pray always that you may be counted worthy to escape all these things that will come to pass, and to stand before the Son of Man. (Luke Luke 21:34-36) [emphasis added]

They were also to watch others in order to guard the fellowship:

Therefore take heed to yourselves and to all the flock, among which the Holy Spirit has made you overseers, to shepherd the church of God which He purchased with His own blood. For I know this, that after my departure savage wolves will come in among you, not sparing the flock. Also from among yourselves men will rise up, speaking perverse things, to draw away the disciples after themselves. Therefore watch, and remember that for three years I did not cease to warn everyone night and day with tears. (Acts Acts 20:28-31)

If they would not watch, then He would come upon them as a thief (Rev. Rev. 3:3+). Unlike the “secure sinner,” those who watch will not be taken by surprise.

strengthen the things which remain
The church of Sardis had need of endurance and was to press forward and strengthen those things which had not already died. Evidently, their fellowship had been drawing back from God’s calling:

For you have need of endurance, so that after you have done the will of God, you may receive the promise: “For yet a little while, and He who is coming will come and will not tarry. Now the just shall live by faith; but if anyone draws back, My soul has no pleasure in him.” (Heb. Heb. 10:36-38)

But the Sardian church would be unable to strengthen the things which remain except for a renewed dependence upon the Holy Spirit. For in their own efforts, they were totally incapable of what Jesus here commands.2 Again we see the purpose for Christ’s title as “He who has the seven Spirits of God” when writing to this dying church.

that are ready to die
The branches were almost completely disconnected from the life-giving vine (John John 15:5).

works perfect
Perfect is πεπληρωμένα [peplērōmena] rather than τέλεια [teleia] indicating works previously prepared and appointed but having been unfulfilled (Eph. Eph. 2:10). The works that they had (Rev. Rev. 3:1+) were done to please or impress men and thus their motivation was fatally flawed. In this, the Sardian church was following in the footsteps of the religious leaders of Jesus’ day: “But all their works they do to be seen by men. They make their phylacteries broad and enlarge the borders of their garments” (Mtt. Mat. 23:5). “Even so you also outwardly appear righteous to men, but inside you are full of hypocrisy and lawlessness” (Mtt. Mat. 23:28).

before God
Before men, the works were impressive and gave the church a name, but before God they were wood, hay, and stubble leaving their appointed true works of God unfulfilled. See Worldly Churches. The NU and MT differ from the TR here having My God . See Revelation Rev. 3:12+.

Notes

1 Donald Grey Barnhouse, Revelation (Grand Rapids, MI: Zondervan Publishing House, 1971), 68.

2 “This doctrine of Total Inability, which declares that men are dead in sin, does not mean that all men are equally bad, nor that any man is as bad as he could be, nor that any one is entirely destitute of virtue, nor that human nature is evil in itself, nor that man’s spirit is inactive, and much less does it mean that the body is dead. What it does mean is that since the fall man rests under the curse of sin, that he is actuated by wrong principles, and that he is wholly unable to love God or to do anything meriting salvation. . . . Man is a free agent but he cannot originate the love of God in his heart. . . . As the bird with a broken wing is ‘free’ to fly but not able, so the natural man is free to come to God but not able.”—Loraine Boettner, The Reformed Doctrine of Predestination (Phillipsburg, NJ: Presbyterian and Reformed Publishing Company, 1932), 61-62.