Doctrines of Men

For I would have you know, brothers, that the gospel that was preached by me is not man's gospel. For I did not receive it from any man, nor was I taught it, but I received it through a revelation of Jesus Christ

Galatians 1:11-12

All such as will have men to preach pleasurable things to their liking, do drive away God as far off from them as they can. True it is that they will not speak after that sort. For even among the Jewish people, every man protested to serve the God that was revealed to their father Abraham, and which had published his law by Moses. Sacrifices were offered in the temple, and there were fair show enough there. Nevertheless the prophet concludes in one word, that men were desirous to be soothed, and fair spoken to, and by means thereof could not suffer God to guide them, nor give him leave to lay his yoke upon their neck. Ye see then theat the means for us to prepared to receive the doctrine of the gospel, and to be edified by the same, is that we be not wedded to our own likings, but suffer our Lord jesus Christ to speak the things that are expedient for our instruction. Howbeit besides this, we must also be as it were wounded to the heart by the word that is preached to us, or else we shall never fare the better for it.

Calvin's Sermons on Galatians, 91

Paul's defense of the source of his doctrine makes it clear that he was being accused of preaching an easy gospel. It seems strange to me, but the Judaiser's claimed that by allowing Gentiles to avoid circumcision and the other strictures of the law, Paul was in fact preaching the doctrines of man and an easy gospel.

It's ironic that circumcision, which was given by revelation, should become a doctrine of man. But in putting their hope in it rather than the free mercy of God, the Jewish people robbed it of its meaning, supposing that God could be pleased if they just went through the motions. That is how it became a doctrine of man.

I can understand their reasoning to an extent: the law of circumcision came as a revelation from God to Abraham and Moses, and so it must be human doctrine to assert that it held no force in the Christian life. But more than anything else, this only showed their ignorance of Christ. For as you said, Frank, the Christian life is not easy - there is no comparison with circumcision; the Christian life requires a constant humbling of our sinful pride, for we always want to imagine that we can please God in our own way. Calvin shows what it means to be humbled by God: that we should welcome his word, even though it slays us. For any injury we receive from God will only strengthen us for his service.