In case you aren't sure what the difference is...I would say...standards and preparation.
For some reason churches have developed the attitude that everyone is welcome to join the choir. That way no one gets their feelings hurt.
That's song leaders, not a choir.
Great music does NOT just happen.
It requires a certain degree of musical ability on the part of the singers, good direction, and adequate rehearsal. Not everyone can sing well. It's not mean or uncharitable to say so, that is a demonstrable fact.
Now that doesn't mean that you have to be a professional vocal musician to join the choir. In fact, I enthusiastically encourage people with no previous experience to join the church choir. If God gave you the ability to sing I can think of no better place to develop that talent than in service to Him. It's been my experience that a church choir is a very supportive environment in which to develop vocal talent.
Point 2: Hold Auditions.
If everyone can match pitch, then everyone gets in.
If someone auditions and can't match pitch, offer to work with them privately for a few weeks. For most, that will be all the additional work required. Very few people are truly tone deaf.
If a person can't match pitch after you've worked with them, then and only then, charitably suggest that they should seek another way to serve the church.
Holding auditions also lets people know that you take music seriously and therefore...so should they. It will set the right tone for all your future efforts to build a good choral program.