Adam Clarke on Proverbs 27:1

Boast not thyself of to-morrow - See note on Jam 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.