Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all… – Romans 4:16
What does the “it” refer to? It is of faith. If you will read the context, I think you will consider that it refers to the promise, although some have said that the antecedent word or thought is, “the inheritance.” This matters very little, if at all—it may mean the inheritance, the Covenant, or the promise, for these are one. To give a wide word which will take in all—the blessedness which comes to a man in Christ, the blessedness promised by the Covenant of Grace is of faith—in one word, salvation is of faith!
And what is faith? It is believing the promise of God, taking God at His word and acting upon that belief by trusting in Him. Some of the Puritans used to divide faith improperly, but still instructively, into three parts. The first was self-renunciation, which is, perhaps, rather a preparation for faith than faith itself. In it a man confesses that he cannot trust in himself and so goes out of self and all confidence in his own good works. The second part of faith, they said, was reliance in which a man, believing the promise of God, trusts Him, depends upon Him and leaves his soul in the Savior’s hands. And then they said the third part of faith was appropriation by which a man takes to himself that which God presents in the promise to the Believer—he appropriates it as his own, feeds upon it and enjoys it. Certainly, there is no true faith without self-renunciation, reliance and at least a measure of appropriation—where these three are found, there is faith in the soul.