The Savior also was holy from the very beginning of his existence. There was no one power, either of body or mind, that was not fully sanctified. But it was said of him, in terms similar to those applied to John the Baptist, Luke 9: 40: "And the child grew, and WAXED STRONG IN SPIRIT, filled with wisdom, and the grace of God was upon him." And again it is said of him, in the same chapter, "And Jesus increased in wisdom and stature, and in favor with God and man." What is the meaning of this increase of strength in spirit? And how could be increase in the favor of his heavenly Father, if, with the increase of his expanding powers, there was not also a corresponding growth in holy love?
The Scriptures every where speak of growth. They do not recognize the idea of standing still; and all those passages, which require growth in grace and religious knowledge, are as applicable after the experience of sanctification as before. "Let us, therefore, as many as be PERFECT be thus minded." Philip. 3: 15. Be thus minded in what respect? The answer is found in the preceding verse, viz., to "press toward the mark for the prize of the high calling of God in Christ Jesus."
"Be ye, therefore, perfect," says the Savior, "as your Father in heaven is perfect." This remarkable and most impressive command evidently implies two things. The first is, that we should be perfect in our sphere; that is to say, in our perceptions, our feelings, and our purposes, to the full extent of our capability. And the second is, that we should continually expand, in accordance with that law of increase which is a part of the nature of every rational being, our capacity of feeling and of knowledge, whatever it may be. And in doing this, (that is to say, on the supposition of its being done,) we fulfill the command absolutely, so far as the nature of our mental exercises is concerned; and fulfill it by approximation, or continual expansion and growth, so far as relates to their degree.
It is thus with the angels in heaven. They are holy; but are always growing in holiness. In the nature of their exercises they are like their heavenly Father, and perfect as he is perfect; but in relation to the degree of their exercises, they can be said to be perfect only in availing themselves of every possible means of approximation and growth.
Growth, therefore, continual advancement, is the unalterable law of all created, holy beings. And hence it is further said in the Scriptures, in expressions that are full of weighty import, "For whosoever hath, to him shall be given, and he shall have more abundance; but whosoever hath not, from him shall be taken away even that he hath." Matt. 13: 19.
— edited from The Interior or Hidden Life (1844) Part 2, Chapter 15.