The church is the body and bride of Christ (1 Cor 12:27; Col 1:24; Eph 5:22-33).
A professing Christian who consistently neglects the fellowship of the church has, at very best, a relationship to Christ that is analogous to a wife trying to have a relationship with her husband only over the phone. Over the phone, a wife may hear her husband's voice [as a Christian may hear the voice of Christ through the private reading of Scripture or through hearing sermons on the radio, etc.], but she will not receive her husband's embrace unless she is physically with him. A wife may have a good cause to be separated from her husband for a lengthy period of time (I think of my aunt, whose husband-- my uncle-- is serving with the Army in Iraq), but if she loves her husband this separation will be considered unusual and she will want to physically be in his presence at the earliest opportunity. Similarly, the Christian may be away from the church by necessity (through disease, etc.), but such separation should be considered unusual; the Christian should long to be with the fellowship the church: Christ's body on earth.