There are several ways in which involvement in your community is considered essential to Christian faith traditions. As stated in the New Testament:
For as the body without the spirit is dead, so faith without works is dead also. (Jas. 2:26)
There are many places where Jesus commands his followers to practice charity, and one can not be considered a faithful Christian without following the path recommended by Jesus; simply giving lip service to Christian belief without actually performing charitable works is to behave like the hypocrites condemned by Jesus in many places in the New Testament.
Next, the Church is a faith community, and acts which strengthen your connections to that community, improve the community as a whole and also give you a strong network of fellow believers to support your faith.