Where and how many times did He say that and how many times are we told to beware of false teachers?
Well Christ did say we'd know false prophets by their actions. St Paul even said that folks who refuse to acknowledge that what he wrote was commandments from God were false prophets yet protestants were founded by murderous folks and in only 400 years of protestantism have managed many firsts such as rejecting St Paul on headcovering and women preachers. Promoting abortion under the guise of helping the poor. Saying that a Christian church can have homosexual clergy. Saying that Christian churches can bless homosexual relations. Meantime they've gone from 5 something denominations to 20000+. Boy wouldn't SATAN want to do all those things?
Now who seriously is leading protestantism? God who is not the author of confusion (As Saint Paul tells us) or Satan who benefits endlessly from the vile things protestants due in the name of God?
See among my recent posts for the obedience to the Church. Yes, we are well aware of the false teachers and this is precisely the reason why we beware of the Protestant teachings.