My son - The preceptor continues to deliver his lessons.
Forget not my law - Remember what thou hast heard, and practice what thou dost remember; and let all obedience be from the heart: "Let thy heart keep my commandments."

My son, forget not my law,.... Or, "doctrine" (e); the doctrine of Christ, the Gospel, and the several truths of it; which, being of the utmost moment and importance, should be kept in memory, and not let slip, or be in the least slighted and neglected; see Hebrews 2:1;
but let thine heart keep my commandments; as the ark, or chest, kept the two tables of the law put into it; it denotes a cordial affection for the commandments and ordinances of Christ, a hearty attention and obedience to them, and a constant and cheerful observance of them, flowing from love and gratitude to him, John 14:15.
(e) "doctrinae meae", Piscator, Michaelis; "institutionem meam", Schultens; "doctrinam meam", Cocceius.

In the way of believing obedience to God's commandments health and peace may commonly be enjoyed; and though our days may not be long upon earth, we shall live for ever in heaven. Let not mercy and truth forsake thee; God's mercy in promising, and his truth in performing: live up to them, keep up thine interest in them, and take the comfort of them. We must trust in the Lord with all our hearts, believing he is able and wise to do what is best. Those who know themselves, find their own understandings a broken reed, which, if they lean upon, will fail. Do not design any thing but what is lawful, and beg God to direct thee in every case, though it may seem quite plain. In all our ways that prove pleasant, in which we gain our point, we must acknowledge God with thankfulness. In all our ways that prove uncomfortable, and that are hedged up with thorns, we must acknowledge him with submission. It is promised, He shall direct thy paths; so that thy way shall be safe and good, and happy at last.

The study of truth commended. God must be feared, honored, and trusted, and filial submission, under chastisement, exhibited. The excellence of wisdom urged and illustrated by its place in the divine counsels. Piety enforced by a contrast of the destiny of the righteous and the wicked. (Proverbs. 3:1-35)
law [and] commandments--all divine instructions (see on Psalm 119:1 and Psalm 119:4).
let thine heart keep--or sincerely observe (Proverbs 4:13; Proverbs 5:2).

My law - The law of God, which might be called his law, as the gospel is called Paul's gospel, 2-Timothy 2:8, because delivered by him.