The notion that evangelism must constantly be plied in the assembly is a misnomer. Many evangelize the saved over and over again in an attempt to reach the lost - forgetting that the main purpose for the assembly of saints is for their edification. The pastors are evangelizing lost while the sheep trusted to their care are starving to death. They forget that it is not what you do for God, but what you are for God. If what you are is right, then what you do will be right, and God will be properly glorified.
Evangelism belongs outside of the church, and edification belongs inside the church.
It is to be the spiritual boot camp for believers to prepare them for battle against worldliness, the flesh, and Satan.