I think the following from Paul's letter to the Romans, chapter 4, explains it very well:
I’m sure paul was very intelligent, but I am dumb and your long post made my eyes gaze over...
I tend to be like Peter who complains he doesn’t always understand Paul’s writings but says you should read them anyway.
However, Jesus tended to teach by using stories, and he is a bit more nuanced in how you are saved. In one verse, he says you are saved if you believe in him. In another, he notes that saying Lord Lord isn’t enough, and in a third one he notes that at the last judgement, some who get to heaven don’t recognize him, but are admitted because he accepts their deeds to the poor as serving Him.
Try reading and praying over the gospels, not taking a verse of Paul out of context and making it the entire truth.
we are saved by grace, but as Paul said: by the grace of God I am what I am, and his grace in me has not been fruitless.