People have different tastes in music. Even those that have a common liking of a particular style of music have different tastes. I know a young lady who celebrated her high school graduation with a cello recital. It was quite good, and I am a fan of classical music, but my taste is more toward opera and symphonies. I like the interplay between large groups of instruments or voices. Solos, such as operatic arias, are good, but they play best in the context of the larger group. Maybe God shares my taste, as well as liking the smaller groups. Maybe that is why he expects Christians to assemble together.
Worship is certainly an individual thing. Each of us must worship God “in spirit and in truth.” (Jn 4:24) We can, and must, worship God individually and consistently. “Pray without ceasing.” (1 Thes 5:17) “By him therefore let us offer the sacrifice of praise to God continually, that is, the fruit of our lips giving thanks to his name.” (Heb 13:15) Since we are not continually in concert with others, God clearly expects our individual and private worship.
We are like God in that. Most of our conversations in life are between two people. We appreciate the virtuoso pianist or the solo cello. But people are also fond of parties. Even the most independent of us likes to mingle with others. There are probably three reasons that people attend cocktail parties. Some go for the liquor. Some go to be seen by others. The appeal of a good cocktail party, however, is the conversation. A good guest can move easily from one conversation to another. Even the wallflower, if he or she is enjoying him(her)self, likes observing the constantly shifting interplay. If conversation is the solo instrument, this shifting of themes and variations between groups is the symphony orchestra. God likes the chamber music (or, to use the term in one translation of Matthew, “closet” music). But he also likes the symphony.
What we often call the church is more properly the assembly. It is a group of people called for a common purpose. While that common purpose includes worship, it also includes encouraging one another (Heb 10:24). In a proper congregation there should be melody and countermelody, theme and variation. It is this interplay of voices and motifs that makes the assembly interesting, and valuable. There may even be an occasional solo or aria in the assembly (most notably a preacher), but the congregational relationship requires receipt and response.
That this communal interaction is pleasing to God is evidenced by Christ’s prayer for unity.
That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. And the glory which thou gavest me I have given them; that they may be one, even as we are one: I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me. (Jn 17:21-23)
Unity is not necessarily unison in the musical sense. It is not everyone singing the same note; it is everyone playing the correct note to create a pleasing whole. Whenever someone breaks this unity by demanding his own way rather than the prescribed score, the unity is broken and the congregation presents discord. “For God is not the author [or composer] of confusion.” (1 Cor 14:33) He expects us to follow his score and not our own.
Unlike some of us, God has varying tastes. He enjoys the trumpet solo of our individual prayers. He also enjoys the orchestration of communal worship. Some people ask why they have to “go to church,” since they can worship God by themselves. That would be like Wynton Marsalis choosing only to play trumpet by himself. The performance would be outstanding, but eventually people would long to hear him with a combo or an orchestra. I suspect he would do so as well. God wants to hear from us individually, but he also enjoys the collective worship and fellowship.