The Body of Christ. The Bride of Christ. The Fellowship. The People of God. This is a sampling of the language sometimes used to describe the Church.
The Church isn't simply a concept or a metaphor. It isn't some faceless group of disconnected people mysteriously joined over space and time by shared belief. For every believer, everywhere, anytime, it is a rag-tag group of specific names and faces. People we share air with. People we know.
And here's the thing, according to every example in the scriptures, it is an absolutely necessary part of following Jesus. In 1st John chapter 4, the apostle writes: "whoever does not love their brother and sister, whom they have seen, cannot love God, whom they have not seen." The Church is not some optional club-of-Jesus-followers we can take or leave. This stuff matters. We literally can't love God alone.