Sentence:  This means that the antennae of the congregation are extended into the community , picking up the wave lengths of those who will fit into the social and economic level of the congregation ; the mission of the church is actually a process of informal co-optation ; the lay ministry is a means to recruit like-minded people who will strengthen the social class <WSD>nucleus</WSD> of the congregation . 
Meaning of the word marked with <WSD> tags:  a small group of indispensable persons or things