Hebrews (Jews), who were either new Christians or were strongly considering Jesus Christ for salvation, in the first century would understand their rejection of Old Covenant worship. If Jesus fulfilled the Old Testament ceremonies and rituals, what would worship be or look like for them? They acknowledged a possible huge variation in their lives, which clashed with their family and ethnicity.
The writer of the book of Hebrews deals with this Hebrew contemplation in Hebrews 10:25. The author instructs his audience in the corporate New Testament worship that replaced the Old. He wrote: “Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.” New Testament worship meant “not forsaking the assembling of ourselves together.”
A church, the institution the Lord Jesus Christ started, is an “assembly” (the Greek, ekklesia). Corporate New Testament worship means “assembling” with the “assembly,” the church. What is “forsaking the assembling of ourselves together”? This is not assembling with the church, when it assembles. Not assembling is forsaking the assembling. This can be seen in some of the following words.
The “manner” of something is the Greek, ethos, which is a practice or habit, a customary behavior. Some got in the habit of missing the assembling. The author Hebrews under inspiration of God warns not to do this, especially with the “day approaching.” The day is the day of Christ’s return, which is a day of judgment for everyone.