Boast not thyself of to-morrow - See note on James 4:13, etc. Do not depend on any future moment for spiritual good which at present thou needest, and God is willing to give, and without which, should death surprise thee, thou must be eternally lost; such as repentance, faith in Christ, the pardon of sin, the witness of the Holy Spirit, and complete renovation of soul. Be incessant in thy application to God for these blessings.
My old MS. Bible translates thus: Ne glorie thou into the morewenning. Here we see the derivation of our word morning; morewenning, from more, and wen or won, to dwelt, i.e., a continuance of time to live or dwell in your present habitation. Every man wishes to live longer, and therefore wishes for to-morrow; and when to-morrow comes, then to-morrow, and so on.

Boast not thyself of to (a) morrow; for thou knowest not what a day may bring forth.
(a) Do not delay the time, but take the opportunity when it is offered.

Boast not thyself of tomorrow,.... Or, "of tomorrow day" (t). Either of having a tomorrow, or of any future time; no man can assure himself of more than the present time; for, however desirable long life is, none can be certain of it; so says the poet (u): for though there is a common term of man's life, threescore years and ten, yet no one can be sure of arriving to it; and, though there may be a human probability of long life, in some persons of hale and strong constitutions, yet there is no certainty, since life is so frail a thing; the breath of man is in his nostrils, which is soon and easily stopped; his life is but as a vapour, which appears for a little while, and then vanishes away; all flesh is as grass, which in the morning flourishes, in the evening is cut down, and on the morrow is cast into the oven: man is like a flower, gay and beautiful for a season, but a wind, an easterly blasting wind, passes over it, and it is gone; his days are as a shadow that declineth towards the evening; they are as a hand's breadth; yea, his age is as nothing before the Lord. Death is certain to all men, as the fruit of sin, by the appointment of God; and there is a certain time fixed for it, which cannot be exceeded; but of that day and hour no man knows; and therefore cannot boast of a moment of future time, or of a tomorrow, nor of what he shall enjoy on the morrow (w); for, what he has today he cannot be certain he shall have the next; he cannot assure himself of health and honour, of pleasures, riches, and friends; he may have health today, and sickness tomorrow; be in honour today, and in disgrace on the morrow: he may bid his soul eat, drink, and be merry, seeing he has much goods laid up for many years, and vainly say, tomorrow shall be as this day, and much more abundant, when this night his soul may be required of him; he may have his wife and children, friends and relations, about him now, and before another day comes be stripped of them all; he may be in great affluence, and gave great substance for the present, and in a short time all may be taken from him, as Job's was; riches are uncertain things, they make themselves wings and flee away. Nor should a man boast of what he will do on the morrow; either in civil things, in trade and business; to which the Apostle James applies this passage, James 4:13; or in acts of charity, so Aben Ezra explains it, boast not of an alms deed to be done tomorrow; whatever a man finds to be his duty to do in this respect, he should do it at once, while he has an opportunity: or in things religious; as that he will repent of his sins, and amend his life on the morrow; that he will attend the means of grace, hear the Gospel, the voice of Christ; all which should be to day, and not be put off till tomorrow. Nor should true believers procrastinate the profession of their faith; nor should any duty, or exercise of religion, be postponed to another season; but men should work while it is day, and always abound in the work of the Lord, and be found so doing; see Isaiah 56:12;
for thou knowest not what a day may bring forth; time is like a teeming woman, to which the allusion is, big with something; but what that is is not known till brought forth: as a woman, big with child, knows not what she shall bring forth till the time comes, whether a son or a daughter, a dead or a living child; so the events of time, or what is in the womb of time, are not known till brought forth; these are the secret things which belong to God, which he keeps in his own breast; the times and seasons of things are only in his power, Acts 1:6. We know not what the present day, as the Targum renders it, will bring forth; and still less what tomorrow will do, what changes it will produce in our circumstances, in our bodies and in our minds; so that we cannot be certain what we shall be, what we shall have, or what we shall do, on the morrow, even provided we have one.
(t) "in die crastino", Pagninus, Montanus. (u) Sophoclis Oedipus Colon. v. 560. "Nemo tam divos habuit faventes, erastinum ut possit sibi polliceri", Senco. Thyest. v. 617, 618. (w) "Quid sit futurum eras, fuge quaerere", Horat. Carmin. l. 1. Ode 9.

We know not what a day may bring forth. This does not forbid preparing for to-morrow, but presuming upon to-morrow. We must not put off the great work of conversion, that one thing needful.

(Proverbs. 27:1-27)
Do not confide implicitly in your plans (Proverbs 16:9; Proverbs 19:21; James 4:13-15).

In the group Proverbs 27:1-6 of this chapter every two proverbs form a pair. The first pair is directed against unseemly boasting:
1 Boast not thyself of to-morrow,
For thou knowest not what a day bringeth forth.
The ב of בּיום is like, e.g., that in Proverbs 25:14, the ב of the ground of boasting. One boasts of to-morrow when he boasts of that which he will then do and experience. This boasting is foolish and presumptuous (Luke 12:20), for the future is God's; not a moment of the future is in our own power, we know not what a day, this present day or to-morrow (James 4:13), will bring forth, i.e., (cf. Zephaniah 2:2) will disclose, and cannot therefore order anything beforehand regarding it. Instead of לא־תדע (with Kametz and Mugrash), אל־תדע (thus e.g., the Cod. Jaman) is to be written; the Masora knows nothing of that pausal form. And instead of מה־יּלד יום, we write מה יּלד יום with Zinnorith. יּלד before יום has the tone thrown back on the penult., and consequently a shortened ult.; the Masora reckons this word among the twenty-five words with only one Tsere.

Boast not - Of any good thing which thou purposeth to do, or hopest to receive tomorrow, or hereafter. Knowest not - What may happen in the space of one day. The day is said to bring forth, what God by his almighty power either causes or suffers to be brought forth or done in it.