Because when you’re absent, you miss more than you gain. Like Thomas. The Gospel of John relates this exchange on the day Jesus rose from the dead after he appeared to the 10 (Judas was dead and Thomas was absent):
Now Thomas, one of the twelve, called the Twin, was not with them when Jesus came. So the other disciples told him, “We have seen the Lord.” But he said to them, “Unless I see in his hands the print of the nails, and place my finger in the mark of the nails, and place my hand in his side, I will not believe.” Eight days later, his disciples were again in the house, and Thomas was with them. The doors were shut, but Jesus came and stood among them, and said, “Peace be with you.” Then he said to Thomas, “Put your finger here, and see my hands; and put out your hand, and place it in my side; do not be faithless, but believing.” Thomas answered him, “My Lord and my God!” Jesus said to him, “Have you believed because you have seen me? Blessed are those who have not seen and yet believe. (Jn. 20:24-29)
Several things are worth noting here. First, Thomas was absent and didn’t get to experience the first appearance of Jesus after he rose from the dead. Absent from the gathering of disciples, one doesn’t have the privilege of experiencing God in a special way. Second, Thomas fell into doubt because of his absence. Doubt creeps in when we are unwilling to gather with others who believe. The more we absent ourselves from worship with other believers, the more we open the door to doubt’s corrosive effects. And third, Thomas got another chance. Being absent once isn’t the end of the world. You may well have another opportunity to encounter Christ in the community of faith if you avail yourself of the opportunity.
What you miss when you miss worship is Christ. Is what you ‘gain’ by staying away more important then being with Him?