Then let us turn once more to Aquinas,
The child Jesus grew in age and wisdom and favor with God and men. http://dhspriory.org/thomas/SermPuerIesus.htm
1. Everything that the Lord did or suffered in the flesh is an instruction and an example for our salvation, and so we find in John: I have given you an example that as I have done, so you should do also; and because the way of salvation is not absent to each age of human life, especially that age corresponding to the years of discretion, Christ's adolescence is proposed as a model for adolescents. Now, since adolescence is characterized by development and growth, Christ's growth is therefore proposed as a model for adolescents. In order that we may be able to say something about Christ's growth that will be to the honor of God and to the salvation of our souls, let us entreat the Lord at the beginning.
The child Jesus, etc.
2. If we wish to consider these words carefully, we will discover in them four aspects of Christ's growth, namely an a growth in age with respect to the body; a growth in wisdom with respect to understanding; a growth in grace with respect to God; and a growth in favor with respect to his fellowship with men.
3. Indeed, all these [different] growths are wondrous, or rather they are filled with astonishment and wonder; indeed it is wondrous that eternity grows by way of time, since the Son of God is eternity and from eternity: For ever, 0 Lord, your word endures.
4. Again, it is wondrous that truth grows by way of wisdom, since growth in wisdom is knowledge of the truth, and Christ truth itself, as we read in John: I am the way, the truth and the life.
5. Again, it is wondrous that the maker of grace grows in grace; indeed Christ is the creator of grace, as [it says] in John: Grace and truth were made through Christ.
6. Again, it is wondrous that he who surpassed all men grows in their presence deserves to be admired; men ought rather to grow in his presence. As the Psalmist says: He is high above all nations. How then will Christ grow in all these ways?
7. I say that if we rightly want to consider his growth in age, one reason comes immediately to mind. The eternal Son of God wished to enter into time so that he would be able to grow according to the ages of human life. [As it says in] Isaiah: A child is born to us. If he was born as a child, why then would he not grow up as a child?
8. The other growths of Christ present a greater difficulty. Christ assumed a complete human nature; he was born a child according to the flesh, but not according to the soul, because from the moment of his conception his most blessed soul, having been united to God, was filled with every grace and truth; as we find in John: We saw his glory, the glory as of the only begotten of the Father, full of grace and truth. He was filled with grace and truth because he was the only begotten of God; but from the moment of conception he was the only begotten; therefore, at that moment he was filled with grace and truth and he was made perfect in virtue. We read in Jeremiah: A woman shall compass a man. This occurred through perfection of mind rather than of age, but how is he said to grow by wisdom and grace?
9. It must be asserted that someone is said to grow in wisdom not only when he acquires greater wisdom but more so when wisdom is revealed within him. It is true that Christ was filled with wisdom and grace from the first moment of his conception,` but he did not reveal it from the beginning, but when others were accustomed to doing so. At that time he is said to have grown in wisdom," not in himself, but with respect to outward results by which he was growing in other areas. If he had wished to show his wisdom when he was seven years old, men could have doubted the reality of his assumed human nature, and for this reason Christ wished to be conformed to other men. Therefore, the Apostle to the Philippians says: He emptied himself, taking the form of a servant, being made in the likeness of men. Christ made himself little by taking on our littleness; and in order that he might truly show himself to be little he was made in the likeness of men. The Apostle says: He was seen on earth and conversed with men, and Christ first revealed his wisdom at that age when wise judgement usually first appears in a person, namely, when he was twelve years old. Therefore, he wished to reveal his wisdom little by little, not [all at once], so that the truth of his human nature within him would be accepted, and so that he might give us an example of growing in wisdom.
10. Therefore, as we have already mentioned, the growth of Christ was fourfold, namely years, wisdom, grace, and in human fellowship.
11. Let us first describe Christ's growth in age, which is bodily, and which is proposed to us as a model in order that we may grow in age of body and mind like him, because a growth in bodily age is worthless if the soul does not keep pace with it; hence Christ's growth in wisdom and grace kept pace with his growth in age. For if a man fails to advance in mind at equal pace with his physical age four incongruities result from it, because this is monstrous, wasteful, burdensome or laborious, and dangerous.
12. Let me begin by saying that growing in age of body but not growing in maturity of mind is monstrous. Man is composed of a soul and a body just as a body is composed of various limbs, but let us suppose that, some body grows in one limb and its growth remains stunted in its other limbs: this is monstrous. The same is true when anyone has the body but not the mind of an adult. For this reason the Apostle says: When I was a child, I understood as a child, I spoke as a child, but when I became a man I put away those things of a child. Children think about play and of other such things. It is true that the Lord commands that we be as little children, saying in Matthew: Unless you be converted and become as little children, you shall not enter the kingdom of heaven. Some childlike qualities we ought to retain, because children are not malicious, but are humble. But other childlike qualities we ought to cast off, because children are lacking in wisdom; hence the Apostle says: Do not become children in understanding. But in malice be children and in understanding be perfect. We ought to bear in mind that inasmuch as we are growing in physical age we should be growing in mind as well. Suppose that someone were to experience growth in one foot and not in the other, he would make every effort to see a doctor so that his other foot would grow in the same manner. In the same way, you who are growing older should make every effort to see that your mind develops too.
13. Furthermore, growing in bodily age but not in maturity of mind is wasteful. Suppose someone had the time to acquire a great object and he allowed it to slip away in vain, he would consider this a great waste. In the same way should either the merchant who believes that he is profiting much at trading time or the student who believes that he is listening to a useful lecture lose that time, he considers himself to have lost much. Time is not given to you for acquiring such paltry things, but for God and the heavenly blessings which no one can take away; hence the Apostle says: Eye has not seen, nor ear heard,. neither has it entered into the heart of man what things God has prepared for them that love him. For this reason it is said: Let not the part of a good time pass you by; and Solomon says: Give not your honor to strangers, nor your years to the cruel, lest strangers be filled with your strength, and your labors be in another's house. Give not your honor to strangers: honor is granted to man for defeating his enemies in war; such honor is granted to you who overcome the world, the flesh, and the devil. But when you offer your natural abilities to serve the devil, which were given to you to defeat the devil, then you are giving your honor away to a stranger. Next follows: Give not the years of your youth to the cruel," that is, to the devil who is cruel, because, inasmuch as it is necessary that you serve him, he will not give you rest; therefore Jeremiah says: You shall serve strange gods, who will not give you any rest. And your labors will be in another's house. Perhaps you are performing good works and have labored on their account; if you are devoted to the Lord, then your labors will be in your house. However, if you are not devoted to the Lord, then your labors will be in a stranger's house because the saints in heaven will be rejoicing over your good works and not you. Therefore, it is said in Revelation: Take hold of that which you have, lest another take your crown.
14. Moreover, growing in bodily age but not in maturity of mind is laborious. But you will say: "I am young; I want to play while I am young; when I grow old I will devote myself to the Lord". To be sure, you are committing yourself to great labor: that which a man has grown accustomed to doing from his youth is easy for him; this is evident because laboring in a field is easy for a farmer, since he has grown accustomed to it, but for you it is difficult. If you grow accustomed to having your own way and to living in your sins, either you lose hope of attaining eternal life or you store up for yourself much labor; therefore Solomon says: A young man will walk according to his way: even when he is old he will not depart from it. And Jeremiah says: It is good for a man, when he has borne the yoke of the Lord from his youth, because such a man can easily overcome difficulties, and therefore Christ has given us an example of doing good from youth, because when he was twelve years old he grew in wisdom.
15. Again, it is dangerous when anyone grows in bodily age but not in maturity of mind. God will require an accounting from everyone; thus we read in the Gospel: The kingdom of heaven is like a man settling an account with his servants. God has given you time so that you may serve Him, but it is said in Job: He has given him time and he has abused it in pride. God will require from you an accounting of your time. Isaiah [says]: And I said.. I have spent my strength without cause and in vain. He uses up his strength uselessly and without good reason who spends his time on worthless things; and therefore this follows in Isaiah: Therefore my judgement is with the Lord, and Solomon says: Rejoice therefore, 0 young man, in your youth, and know that for all these God will bring you into judgement. Will that be an easy judgement? No, because as Isaiah says: The child being one hundred years old will be accursed, that is, a sinner. Whence it says in Baruch: You have grown old in a foreign country; you are counted with them that go down to hell. But refuse to despair of God's mercy even though your deserts warrant this.
16. This then is our first concern, that we should mature in mind just as in age. But how does man mature in mind? Surely when he matures in wisdom and grace, and, although Thessalonians mentions wisdom before grace, we will nevertheless discuss grace first, since the fear of the Lord is the beginning of wisdom.