I am shocked that you are turning away so soon from God, who called you to Himself through the loving mercy of Christ. You are following a different way that pretends to be the Good News but is not the Good News at all. You are being fooled by those who deliberately twist the truth concerning Christ.
(Galatians 1:6-7 NLT)

Now to the other side of the question. In church-world today, I hear folks applying the “legalism” accusation to lots of things that are simply not. Apart from salvation, most of the Bible’s promises have conditions. It is not legalism to report the teaching of Scripture concerning the pre-requites for receiving a conditional promise. Give and it shall be given to you: No give, no receive. (Luke 6:38) If you don’t renew your mind, you will not be transformed and live out the will of God. (Romans 12:2) If you want to experience supernatural peace, then stop worrying, start praying, and get grateful. (Philippians 4:6-7). Hopefully, you get the point. If you’re not seeing the “then” of God’s promise, maybe you’re not doing the “if.”