Protestant doctrine says that salvation comes by mere faith that Jesus is the son of God, who died on the cross for our sins. James disagreed when he wrote “people are justified by works, and not by faith alone”. Moreover, the claim of that faith alone is the key to salvation also directly contradicts the teachings of Jesus himself:
Not every one who calls me Lord shall enter the kingdom of heaven; only those who do the will of heaven. Many will say to me on that day “Lord, have we not prophesied, cast out devils, and done many wonderful works in your name?” Then will I profess to them “I never knew you: depart from me, you who work iniquity.”
Whoever hears my teaching and follows it is like a wise man who builds his house upon rock. When the rain descends and the floods come, and the winds blow, and beat upon that house, it will not fall: for it was founded upon rock. But those who hear my teaching and ignore it are like fools who build their houses on sand: When the rain descends, and the floods come, and the winds blow, and beat upon them, their houses will fall.
Faith is not enough. Remember:
Unless your righteousness surpasses that of the devout and that of the rabbis, you will not enter the kingdom of heaven – Matthew 5:20