Of course, the Christian grows. Jesus Himself grew as a human being, in wisdom and stature and in favor with God and man. It is a great law of the natural and spiritual kingdoms. First the blade, then the ear, then the full corn in the ear. In first John, you find repeated mention of little children, young men and fathers, 1:e., different grades and stages of Christian life. "Desire the sincere milk (or spiritual milk, Rev. Ver.) of the Word that ye may grow thereby (i Pet. 2:-2; i Cor. 3:1-6; Heb. 5:12, 13). A man may have been a Christian for years and yet be only a little, puny babe in Christ.
It is a most blessed privilege that we may depend on our gracious God and Saviour to direct our paths and supply our needs.
The old man or our old man which is spoken of as crucified with Christ I understand to be the man. I, myself, as I was born, a descendant of fallen Adam, an individual reproduction, a living specimen of the old stock, with a selfish perverted will, a darkened mind, unholy affections, corrupt tastes-dead in trespasses and sins; as such a man I had a perverted, diseased, degenerate nature.
I, that old man, died, was crucified (Rom. 6:6) with Christ; I live no more, Christ liveth in me, a new self substituted in place of the old I. Now although the old I is dead and gone before God and for faith, yet the old nature is left behind, is here with its evil tendencies and desires. It wants to do this and does not want to do that. It is ready to flare up and get hot, or get cold and indifferent, to stuff itself with anything that tastes good, and to gratify or indulge any desire or appetite that is excited for the time being. But the new man is a human being of a Christly, Divine order. Christ in you, with a nature that is marked by love, joy, peace; that is gentle, patient, etc. One nature is fleshly, the other is spiritual. One wants to do just as it pleases, the other just as the Lord pleases.
These are contrary the one to the other, and if left to fight it out between themselves the old nature will get the upper hand.
But God by His Spirit, through the Word, teaches us that "our old man has been crucified with Christ." That Christ "died unto sin once," and rose again and "liveth unto God," and that we, who are His, are to reckon ourselves to be dead to sin by His death and alive to God with His life, by reason of the fact that we are in Him now by new birth as we were once in Adam by the first birth. And we are not to let the sin (to which we died in Christ our substitute) have dominion over us, but yield ourselves unto God as alive from the dead, and let Him have control of us and rule us by His own almighty loving Spirit.
Not only that but being dead to sin, and dead to law (by the body of Christ), we are married to another, even to Him that was raised from the dead, joined to the Lord (by the one Spirit by whom we are baptized into one body) and are now one spirit (Rom. 7:1-6; i Cor. 12:12, 13). Depending on our adorable Lord and Head, occupied with Him, we bring forth fruit unto God. And thus though sin the old slave master is present, yet his authority and power over us are gone. We know the truth (the truth of Christ as our precious Redeemer, Deliverer, Emancipator. We know Him as the truth, and the way, and the life) and the truth has made as free. Hallelujah.