Must? A "must" always implies a condition to be met or avoided; an "or else." To what condition
R U referring??? An open-ended vague question like that, as Deb 13 said, I think, is invalid for arriving at ANY credible conclusions due to the variety of interpretations of what you ask due to its vagueness and variety of consequential responses addressing different issues.
Are you asking "Are we commanded to?" or "If we don't are we a "non-Christian?" or "If we don't are we cursed forever?" or "If we don't will we lose our way?" or "If we don't will we lose our power?" or etc.
We are given an imperitive command to "not forsake the assembling together of yourselves." (KJV, I believe) If one is splitting hairs as the lawyer who asked the question of Jesus which prompted the parable of the "Good Samaritan" (And who is my neighbor?) then one may say that the assembling together could a a wide variety of choices and not just church. I guess one has to examine what was meant by the phrase by searching out what it meant to Christ and the ealry church: What did they do? Examine the "Acts" of the Apostles.
Additionally in Hebrews 10:25 the Apostle Paul instructs us, "Let us not give up meeting together, as some are in the habbit of doing, but let us encourage on another---and all the more as you see the Day approaching."
Some might say that meeting online with no eyes to look in and noone to touch or hold or embrace and no body language to observe and no intonations and/or inflections of voice to hear satifies the assembling or meeting together. Personally, I don't think it comes close, but it is better than nothing. So many times is my dry sense of humor mistaken for something which wasn't even in my mind and other things I say in a terribly misunderstood way; all because we weren't communicating in person. But I have noticed that many like the ambiguity as it affords them the opportunity to not be held accountable for what they REALLY think or feel; which is only hurting them.
Church is not just for assembling together for fellowship. It is to fullfill the Great Commision, to be taught from the Word of God, to provide a system of organization for all that we should be about, to worship the Lord en mass, an outlet for our gifts, talents, and abilities, a place to grow and develop in our Christian life, an advocate in facing the world, a family to help us in the raising and nurturing of our children in the Lord, and on.
That being said, I don't go and haven't gone consistanly for about two years now. We are in the process of a move and of the two primary reasons for the move, and this being the most critical for me, finding a church where we can feel as part of the family and actually be a viable part of the family is one. I do have some very sad history with the church and if you had read JimJib's (my previous username whose acct and posts are gone) stories about the two different churches of which my wife and I were hurt you'd understand our delima (please don't ask.) Our ability to trust in the perogatives of the heigharchy (sp?) of the church has been all but destroyed. Consequentially, we do not want to waste any more of our time, gifts, efforts, money, resources (all gifts from God we are accountable to Him for how we invest.) We are hoping that this move to a much larger, consequentially less ethnocenctric (in the general social sense; less clickish or redneckish), area will afford us the opportunity to find another church family of which to belong.
But I do KNOW that I should be in church regularly. There is no greater feeling than being a member of one and integrated into its livlyhood. Christ told us that our bond with Him and consequentially with each other should be stronger than blood family. When someone told Jesus he couldn't go with Him right away because he wanted to bury a blood family menber, his father?, Jesus told him to forget it and come with Him (let the dead bury the dead, I believe.)