“These are grumblers, complainers, walking according to their own lusts; and they mouth great swelling words, flattering people to gain advantage.”
These are grumblers,
A “grumbler” is a chronic complainer. False teachers come into a local congregation with complaints about its teaching. They are critical of those who teach the truth.
These people criticize the doctrine taught itself. All this is an attempt to neutralize those who teach the truth.
walking according to their own lusts;
Religionists’ main motive is their own “lusts.” It may be lust for praise, for novelty, for power, or for social approbation. This is probably social approbation because of the next phrases.
and they mouth great swelling words, flattering people to gain advantage.
False teachers have a large vocabulary. There is nothing wrong in itself with a large vocabulary when it expresses true or exact thought. However, their objective was to impress people with their teaching. In their teaching, they catered to the prevailing opinion.
A sign of false teachers is their complaint about true teaching.
Congregations need to beware of those who would undermine the pastor of the local church, especially doctrinally. The habit of grumbling might lead us into false teaching.
Do not grumble against one another, brethren, lest you be condemned. Behold, the Judge is standing at the door! Jas 5:9