You think you have to just believe in God and that’s it? Let me remind you, even devils do that. The verse you provided doesn’t represent the point he was making. He was talking about Abraham who was righteous without circumcision. What Paul didn’t mention is this: after circumcision came the Israelites were absolutely required to do it 100%, no exceptions, because their work was required for righteousness.
The main things that have changed in the New Covenant is that the temple laws are gone and animal sacrifices are no more. Now there is a perfect sacrifice, Jesus, who can atone for sins permanently. Provided you have faith in him, are repentant, and persist in being obedient to God then you won’t be a branch that is cut off. It’s absolutely quid pro quo.
Romans 11
17If some of the branches have been broken off, and you, though a wild olive shoot, have been grafted in among the others and now share in the nourishing sap from the olive root,
18do not consider yourself to be superior to those other branches. If you do, consider this: You do not support the root, but the root supports you.
19You will say then, “Branches were broken off so that I could be grafted in.”
20Granted. But they were broken off because of unbelief, and you stand by faith. Do not be arrogant, but tremble.
21For if God did not spare the natural branches, he will not spare you either.
22Consider therefore the kindness and sternness of God: sternness to those who fell, but kindness to you, provided that you continue in his kindness. Otherwise, you also will be cut off.
23And if they do not persist in unbelief, they will be grafted in, for God is able to graft them in again.
24After all, if you were cut out of an olive tree that is wild by nature, and contrary to nature were grafted into a cultivated olive tree, how much more readily will these, the natural branches, be grafted into their own olive tree!