Be watchful - Be wakeful; be attentive and earnest - in contradistinction from the drowsy condition of the church.
Strengthen the things which remain - The true piety that still lives and lingers among you. Whatever there was of religion among them, it was of importance to strengthen it, that the love of the Saviour might not become wholly extinct. An important duty in a low and languishing state of religion is, to "strengthen the things that still survive." It is to cultivate all the graces which do exist; to nourish all the love of truth which may linger in the church; and to confirm, by warm exhortation, and by a reference to the gracious promises of God's word, the few who may be endeavoring to do their duty, and who, amidst many discouragements, are aiming to be faithful to the Saviour. In the lowest state of religion in a church there may be a few, perhaps quite obscure and of humble rank, who are mourning over the desolations of Zion, and who are sighing for better times. All such it is the duty of the ministers of religion to comfort and encourage; for it is in their hearts that piety may be kept alive in the church - it is through them that it may be hoped religion may yet be revived. In the apparent hopelessness of doing much good to others, good may always be done to the cause itself by preserving and strengthening what there may be of life among those few, amidst the general desolation and death. It is much to preserve life in grain sown in a field through the long and dreary winter, when all seems to be dead - for it will burst forth, with new life and beauty, in the spring. When the body is prostrate with disease, and life just lingers, and death seems to be coming on, it is much to preserve the little strength that remains; much to keep the healthful parts from being invaded, that there may be strength yet to recover.
That are ready to die - That seem just ready to become extinct. So, sometimes, in a plant, there seems to be but the least conceivable life remaining, and it appears that it must die. So, when we are sick, there seems to be but the feeblest glimmering of life, and it is apparently just ready to go out. So, when a fire dies away, there seems but a spark remaining, and it is just ready to become extinct. And thus, in religion in the soul - religion in a church - religion in a community - it often seems as if it were just about to go out forever.
For I have not found thy works perfect before God - I have not found them complete or full. They come short of what is required. Of what church, of what individual Christian, is not this true? Whom might not the Saviour approach with the same language? It was true, however, in a marked and eminent sense, of the church at Sardis.

Be watchful - Ye have lost ground by carelessness and inattention. Awake, and keep awake!
Strengthen the things which remain - The convictions and good desires, with any measure of the fear of God and of a tender conscience, which, although still subsisting, are about to perish, because the Holy Spirit, who is the author of them, being repeatedly grieved, is about finally to depart.
Thy works perfect - Πεπληρωμενα· Filled up. They performed duties of all kinds, but no duty completely. They were constantly beginning, but never brought any thing to a proper end. Their resolutions were languid, their strength feeble, and their light dim. They probably maintained their reputation before men, but their works were not perfect before God.

Be watchful, and strengthen the things which remain, that are (c) ready to die: for I have not found thy works perfect before God.
(c) Other things, whose state is such, that they are now going, and unless they are confirmed, will perish without delay.

Be watchful,.... Which may respect both ministers and members: the ministers of the Gospel, whose business is to watch over themselves, their conversation and doctrine, and watch every opportunity to preach it, and the success of their ministry; and that they do not grow careless, or be drawn aside through frowns or flatteries; and over others, as shepherds do, to know the state of their flock; as watchmen of cities to give the time of night, and notice of approaching danger; and to see that the laws of Christ's house are put in execution: and this may also respect the members of these churches, who ought to be watchful, and constant attenders on the word and ordinances, and in the duty of prayer; and should watch over themselves, their hearts, thoughts, affections, words, and actions, and against sin, Satan, the world, and false teachers: or "be awake"; which shows that both ministers and churches are asleep, or much inclined to it; which is the present case of both in this period of time:
and strengthen the things which remain, that are ready to die; not good works; though these may be said to be ready to die when men grow weary of them, are lifeless in the performance of them, and want zeal for them; and may be said to be strengthened when men do their first works: nor the graces of the Spirit; for the whole work of grace remains, and though it is imperfect, yet no part is, or can be taken away from it; yea, there is an increase of it, though it may not be discerned; the work of grace cannot die, or be ready to die; there may be a decline as to the exercise of it, and a want of liveliness in it; and things may be ready to die in appearance, and in the apprehension of believers, but not in reality; and besides it is God's work, and not man's, to strengthen this: therefore they may intend the truths of the Gospel, which at the beginning of the Reformation were revived, and were preached with great life and liveliness; but towards the close of this state, as now, would be just ready to expire, to be almost lost, and dead, and buried, as they are; and which it becomes both ministers and members of churches to hold, and hold up, establish, and confirm: or else the rest of the members of this church may be meant, those of them that remained, that were not wholly sunk and apostatized; and yet were in a very faint and sickly state, scarce any life in them, ready to give up their religion and profession; which should be strengthened, by preaching the pure Gospel, by faithfully administering the ordinances of it, and by speaking comfortable and encouraging words to them. The Complutensian edition and some copies read, "which thou art about lose"; which seems a good reading; and the Arabic version, and some other copies, "which thou art going to reject":
for I have not found thy works perfect before God; meaning that the reformers, and reformed churches, stuck where they first began; and did not carry their works neither with respect to doctrine, and especially with respect to discipline and worship, to a greater perfection, as they ought to have done: and however perfect they might appear before men, they were not so in the sight of the omniscient God, nor found so by Christ, before whom all things are naked and open: the Arabic version reads, "before me"; and the Alexandrian copy, the Complutensian edition, the Vulgate Latin, Syriac, and Ethiopic versions, read, "before my God". This church, though she has departed from the corrupt church of Rome, and from her evil doctrines and practices; yet did not go on to that perfection which might have been expected and desired, and which would have rendered her praiseworthy, whereas she is now discommended. It is an observation of a Jewish writer (h), that "if one departs from an evil way, and does not do that which is good, he does not , "make his work perfect", and he is not pronounced blessed.
(h) R. David Kimchi in Psal. i. 2.

Be--Greek. "Become," what thou art not, "watchful," or "wakeful," literally, "waking."
the things which remain--Strengthen those thy remaining few graces, which, in thy spiritual deadly slumber, are not yet quite extinct [ALFORD]. "The things that remain" can hardly mean "the PERSONS that are not yet dead, but are ready to die"; for Revelation 3:4 implies that the "few" faithful ones at Sardis were not "ready to die," but were full of life.
are--The two oldest manuscripts read, "were ready," literally, "were about to die," namely, at the time when you "strengthen" them. This implies that "thou art dead," Revelation 3:1, is to be taken with limitation; for those must have some life who are told to strengthen the things that remain.
perfect--literally, "filled up in full complement"; Translate, "complete." Weighed in the balance of Him who requires living faith as the motive of works, and found wanting.
before God--Greek, "in the sight of God." The three oldest manuscripts, Vulgate, Syriac, and Coptic, read, "before (in the sight of) MY God"; Christ's judgment is God the Father's judgment. In the sight of men, Sardis had "a name of living": "so many and so great are the obligations of pastors, that he who would in reality fulfil even a third of them, would be esteemed holy by men, whereas, if content with that alone, he would be sure not to escape hell" [JUAN D'AVILA]. Note: in Sardis and Laodicea alone of the seven we read of no conflict with foes within or without the Church. Not that either had renounced the appearance of opposition to the world; but neither had the faithfulness to witness for God by word and example, so as to "torment them that dwelt on the earth" (Revelation 11:10).

The things which remain - In thy soul; knowledge of the truth, good desires, and convictions. Which were ready to die - Wherever pride, indolence, or levity revives, all the fruits of the Spirit are ready to die.