“that we are somehow better people”
This, I think, is one way that self-righteousness insinuates itself into a church. And self-righteousness not only deters you from truly being a servant, in the long run, it will turn you into a monster, even if you’re actually right (look what self-righteousness did for the scribes and Pharisees). (Note that actually being right isn’t a defense against a charge of self-righteousness – if anything, actually being right might make you more susceptible to that sin).
I think this is why there is such an emphasis in scripture on humility – it keeps a firm commitment to the Lord from being diverted to a monstrous self-righteousness.