Verse 15 emphasizes ungodliness. These false ministers are the total opposite of what God is, and if we know what God is—what godliness is—then we can identify and avoid them.
Jude then gives four more descriptors to help us identify false teachers: 1) They are discontented murmurers and complainers. They always have something to gripe about. Discontent with their lot in life, they find fault with everything. Nothing is ever right for them. 2) They live to satisfy their every desire, a trait Jude has already explained thoroughly. 3) They speak bombastic bragging words, and 4) they are respecters of persons, if it will benefit them. They will do anything to get ahead.
In verse 17, we were warned that such people will enter the church and try to ruin it, so we have no excuse. They are here already, and we need to make sure they do not stay here by keeping an eye out for them and giving no quarter to them when they begin their ungodly work.
Jude then gives three final descriptions of them in verse 19. He calls them 1) "sensual" or worldly. They are based totally in this world, in the realm of the five senses. They have no connection to the heavenly. 2) They "cause divisions," meaning when they appear, the congregation begins taking sides. 3) He ends his description with the opposite of his description of true church members in verse 1: False teachers do not have God's Spirit. They are not of us. They may be among us, but they are not God's spiritual children (Romans 8:9-17). We can see from their fruits that the spirit they have is not God's.