That word "assembling" is a translation of yet another form of the word "synagogue." It is episynagōgē (ἐπισυναγωγή).
I do not know what value each of you place on the fellowship of God's Church, especially in countries where the choices seem endless, and where it is so free and easy to gather together. Unlike the ancient Christians under the Roman persecution before 313 AD, and unlike many Christians in various countries where the Church suffers persecution, modern western Christians do not take a risk or pay a high price for the opportunity to assemble. But, to understand the value everyone ought to place on the fellowship of God's holy Church, let us summarize the points we have learned in this brief study.
When we gather as the Church we gather with Christ Himself. If we do not so gather or assemble together, we scatter and become prey for the enemy. If anyone doubts the reality of that peril, let us look at the very next verse from the portion we have quoted of the Epistle to the Hebrews. Vs. 26, 27 tell us, "For if we sin willfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, but a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries." Why does the writer, under the inspiration of the Holy Spirit, warn that forsaking the assembling together of the Church leads to a state of willful sin? Need we really ask this question?
When we gather as the Church we have fellowship. This is not merely social; more than that it is also sacramental and theological. That it is sacramental is obvious, as we have seen from the passage about the communion of Christ's Body and Blood. That it is theological is obvious, because of what John tells us about the doctrine of the Apostles who touched, who heard and who saw the Incarnate Christ (especially as they again touched, heard and saw Him after He had risen from the dead). Our fellowship and communion is in the truth of God's word and it is sacramental. It is with God, and it is with one another. Across barriers of time, we have fellowship with the Apostles themselves by believing their testimony and doctrine; this fellowship is with God and with His Son. We have communion with Christ's Body and Blood; we have fellowship one with another; together we look forward to the day when we may be partakers of the Divine nature.
I hope you are not planning to sleep late this Sunday.