Hebrews 10:25

assembling of ourselves together--The Greek, "episunagoge," is only found here and Th2 2:1 (the gathering together of the elect to Christ at His coming, Mat 24:31). The assembling or gathering of ourselves for Christian communion in private and public, is an earnest of our being gathered together to Him at His appearing. Union is strength; continual assemblings together beget and foster love, and give good opportunities for "provoking to good works," by "exhorting one another" (Heb 3:13). IGNATIUS says, "When ye frequently, and in numbers meet together, the powers of Satan are overthrown, and his mischief is neutralized by your likemindedness in the faith." To neglect such assemblings together might end in apostasy at last. He avoids the Greek term "sunagoge," as suggesting the Jewish synagogue meetings (compare Rev 2:9). as the manner of some is--"manner," that is, habit, custom. This gentle expression proves he is not here as yet speaking of apostasy. the day approaching--This, the shortest designation of the day of the Lord's coming, occurs elsewhere only in Co1 3:13; a confirmation of the Pauline authorship of this Epistle. The Church being in all ages kept uncertain how soon Christ is coming, the day is, and has been, in each age, practically always near; whence, believers have been called on always to be watching for it as nigh at hand.

— Jamieson-Fausset-Brown Commentary (public domain)