Romans 4:3

For what saith the, Scripture? Abraham believed God, and it--his faith. was counted to him for righteousness-- (Gen 15:6). Romish expositors and Arminian Protestants make this to mean that God accepted Abraham's act of believing as a substitute for complete obedience. But this is at variance with the whole spirit and letter of the apostle's teaching. Throughout this whole argument, faith is set in direct opposition to works, in the matter of justification--and even in Rom 4:4-5. The meaning, therefore, cannot possibly be that the mere act of believing--which is as much a work as any other piece of commanded duty (Joh 6:29; Jo1 3:23) --was counted to Abraham for all obedience. The meaning plainly is that Abraham believed in the promises which embraced Christ (Gen 12:3; Gen 15:5, &c.), as we believe in Christ Himself; and in both cases, faith is merely the instrument that puts us in possession of the blessing gratuitously bestowed.

— Jamieson-Fausset-Brown Commentary (public domain)