There are two ways to keep members of the church "faithful."
The first way is to be sure everyone is involved. Have a project for each member, and make sure that he feels important in his role. Praise him for the good job he is doing. Make him feel needed; make him feel that the well-being of the whole congregation rests firmly on his shoulders. That will keep him "faithful."
There are two problems with this method. In the first place, it encourages the creation of projects that are not remotely related to the work of the local church. One member plays on the church ball team; another leads the Boy Scouts troop; another is an active member of the "Dorcas Society"; another plans the program for the men's luncheon. Everybody is busy all right, but in activities that are not authorized in the New Testament.
In the second place, members are often given roles for which they are not qualified. A lady is chosen to teach a class, not because she is qualified, but because she needs to be involved. A man is appointed a deacon to help him to be "faithful." Another man is appointed to serve the Lord's Supper for a month in order to encourage him to be present each Sunday that month. This method thus places "the cart before the horse," for no one should ever be assigned any work in the Lord's service who is not already faithful and qualified for the work to be done (2 Tim. 2:2).
The second way to keep people faithful is to develop within them a genuine love for the Lord. When people love the Lord, they will be faithful, and it won't take some kind of "special" project to keep them faithful. They will also be involved: in worship, in study, in prayer, in godly living, in sharing the gospel with a friend, in helping the needy. I have known literally hundreds of Christians who have never in their lives been appointed to any special work, but whose love for the Lord alone keeps them faithful. There is no superficial faithfulness on the part of these; theirs is a faithfulness that is real.
Special responsibilities are fine for those who are qualified, but the man who requires some special duty to be faithful has never learned what true faithfulness is.