Confession with the mouth is the first bodily work unto salvation, but it is not the first work we do to be saved.
Nevertheless I have somewhat against thee, because thou hast left thy first love. Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent.
What is our first love, but Him that first loved us? And what is the first work of loving God, but purifying our hearts by faith unto righteousness. The Ephesians had departed the purifying work of the spirit within to only be doing the outward righteousness of the flesh. They had become Pharisee Christians.
Our first work unto salvation and justification with Christ therefore, is by our spirit working with Christ through faith unto confession with the mouth. It is our spiritual work in believing from the heart unto righteousness of God.
No man believes with the heart unto righteousness, without also resisting the thoughts and intents of the mind unto sin. Faith alone sown in the heart by hearing only, does not spiritually exercise the faith unto righteousness.
The carnal minded doctrine and gospel of dead faith alone, does not acknowledge the things of the spirit and soul of man, that we must work by faith inwardly first to work by faith outwardly in the flesh.
Being created in the image of God is having power of the spirit to think, intend, and imagine with the heart, just as God does, as well as His created angels.
Our thoughts, intents, and imaginations are our spirit at work, which is called having our mind at work by natural man. Our words and deeds of the body are only manifestation of our spirit, that works either with God unto doing righteousness as he, or with the devil unto doing unrighteous works of the flesh as he.
Not only are our words works to be judge by, but Jesus declares the working of our spirit is judged first:
But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Lusting is a work of man's corrupted spirit, and is judged as a work of the flesh by the Lord.
So, although our spirit is first at work with the Spirit of God, to believe with the heart unto righteousness, God still commands us to confess His Son the Lord Jesus with our mouth to be saved, so that the faith of our heart is made complete and whole with our body.
Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar? Seest thou how faith wrought with his works, and by works was faith made perfect?
What is inside alone, is dead, until what it outside in word and deed proves it is there. The doctrine of man's dead faith alone, says something alive is there, that no man can hear nor see. If man can't see and hear our faith, then God won't save and justify by it.