In connection, therefore, with our general doctrine, that faith is the source of feeling both natural and religious, and that it is the great foundation of the religious life, we proceed to say further, that one of the remarkable results of faith, considered as the means of spiritual restoration and renovation, is, that it frees us from that condemnation, which is brought upon us by reason of sin. In other words, we are JUSTIFIED by faith.
Believing themselves to be sinners, believing Jesus Christ to be the propitiation for sins, and accepting salvation through his merits alone, men are forgiven, and are treated, in reference to the law of God, as if they had not sinned against it. In other words, they are justified. The creature, who has violated the divine law, is the subject of justification; God, in connection with the administration of his government and the arrangement of his providences, is the author of it; but still, being justified in the manner which has been mentioned, viz.: by trusting in Christ alone, men are properly said to be justified by faith.
Nor is there any other way of its being done. Justification, in the scripture sense of the term, always implies forgiveness or pardon. Forgiveness or pardon, as the terms themselves imply, is a free gift. At the same time, such are the relations existing among moral beings, that such forgiveness cannot, in the spiritual sense, be made available to the subject or recipient of it without confidence or faith existing on the part of such subject towards the author. A pardon, which is spiritually available, one which is desirable and valuable in the spiritual or religious sense, is a pardon, which results in entire reconciliation between the parties. But it is self-evident, if we could suppose forgiveness or pardon to exist without faith or confidence on the part of the subject of it, (for instance, without faith in the kind intentions of the being offering the pardon and without faith in his power of making it good,) that it would fail to result in mutual reconciliation, in the reciprocation of benevolent feelings, and in true happiness. On a favorable construction of it, it would be merely forgiveness intentional and inchoate; existing exclusively in the mind of the author; without counterpart, and without completion. From the nature of the case, therefore, a man cannot be pardoned or forgiven, to any available spiritual purpose, without faith; and consequently he cannot be justified without faith.
— edited from The Life of Faith (1852) Part 1, Chapter 8.