But his delight is in the law of the LORD; and in his law doth he meditate day and night.

But his delight is in Jehovah's law, and in his law doth he meditate day and night.

But, in the law of Jehovah is his delight, And in His law he doth meditate by day and by night:

But whose delight is in the law of the Lord, and whose mind is on his law day and night.

but his delight is in the law of the LORD, and on his law he meditates day and night.

But his delight - His pleasure; his happiness. Instead of finding his happiness in the society and the occupations of the wicked, he finds it in the truth of God. The law or truth of God is not distasteful to him, but he so delights in it as to desire to become more and more acquainted with it, and to have its truths impressed more and more on his heart.
In the law of the Lord - The law of Yahweh - the small capitals in the translation indicating here as elsewhere that the original word is Yahweh. The word law in the Scriptures is used in a considerable variety of significations. The Hebrew word תורה tôrâh, properly means instruction, precept; and then, an injunction, command, law, in the usual sense of the word. It was applied particularly to the Pentateuch, or law of Moses (compare the notes at Luke 24:44), as containing the first written and recorded laws of God; and then the word came, in a more general sense, to be applied to all the books of the Old Testament, as being an exposition and application of the law. Here the word undoubtedly refers to the written revelation of the will of God as far as it was then made known. On the same principle, however, the declaration here made would apply to any part of a divine revelation; and hence, the sentiment is, that a truly pious man finds his highest delight in the revealed truths of God. This is often referred to as characteristic of true piety. Compare Psalm 19:10; Psalm 119:97, Psalm 119:99.
And in his law - On his law, or his truth. "He doth meditate." The word used here, הגה hâgâh, means properly to complain, to mutter; then, to speak; then, to utter in a low complaining voice, as is often done by a person in deep meditation; hence, in the usual sense, to meditate on anything; to think of it. So Joshua 1:8 : "Thou shalt meditate therein (the law) day and night." Psalm 77:12 : "I meditate on all thy work." Proverbs 15:28 : "the heart of the righteous meditateth what to answer." The meaning here is, he thinks of it; he endeavors to understand its meaning; he has pleasure in reflecting on it. It is not a subject which he puts away from him, or in respect to which he is indifferent, but he keeps it before his mind, and has satisfaction in doing it.
Day and night - That is, continually - as day and night constitute the whole of time. The meaning is:
(a) he does this habitually, or he intentionally forms the habit of meditating on divine truth, by disciplining his mind in order that he may do it;
(b) he takes time to do it - designedly setting apart suitable portions of each day, that, withdrawn from the cares of life, he may refresh his spirit by contemplating divine truth, or may become better acquainted with God, and with his duty to him, and may bring to bear upon his own soul more directly the truths pertaining to eternal realities;
(c) he does this in the intervals of business, the moments of leisure which he may have during the day - having thus an unfailing subject of reflection to which his mind readily reverts, and in which, amid the cares and toils of life, he finds relaxation and comfort; and
(d) he does it in the wakeful hours of night, when sick and tossed upon his bed, or when, for any other reason, his "eyes are held waking." Psalm 63:5-6 : "my soul shall be upon my bed, and meditate on thee in the night-watches." Psalm 119:54 : "Thy statutes have been my songs in the house of my pilgrimage." Compare Psalm 119:23, Psalm 119:43; Psalm 143:5. It is probable that the psalmist had the injunction in his mind which is contained in Joshua 1:8.

But his delight is in the law of the Lord - חפצו chephtso, his will, desire, affection, every motive in his heart, and every moving principle in his soul, are on the side of God and his truth. He takes up the law of the Lord as the rule of his life; he brings all his actions and affections to this holy standard. He looketh into the perfect law of liberty; and is not a forgetful hearer, but a doer of the word; and is therefore blessed in his deed. He not only reads to gain knowledge from the Divine oracles, but he meditates on what he has read, feeds on it; and thus receiving the sincere milk of the word, he grows thereby unto eternal life. This is not an occasional study to him; it is his work day and night. As his heart is in it, the employment must be frequent, and the disposition to it perpetual.

But his delight [is] in the law of the LORD; and in his (b) law doth he meditate day and night.
(b) In the holy scriptures.

But his delight is in the law of the Lord,.... Not the law of nature, which was inscribed on Adam's heart in innocence, but now greatly impaired by sin, and become very imperfect and very insufficient to make men happy, or to lead them to true felicity; nor the law of Moses, which is a fiery law, and works wrath, accuses of sin, pronounces guilty, curses and condemns to death; and therefore cannot be delighted in by a sensible sinner, unless as it is in the hands of Christ, and as fulfilled by him, who is the end of it; and as it is written on the heart of a regenerate man, who, so far as it is, delights in it after the inward man, and serves it with his spirit: but rather the Scriptures, as much and as many parts of them as were written in David's time; particularly the five books of Moses, which are called the Law and the Testimony of the Lord; which being inspired by God, were profitable and delightful to read, and to hear explained; and as they were David's delight, and the men of his council, Psalm 119:24; so they were the delight of every good man, there being many things in them concerning the Messiah, his grace and kingdom; see Luke 24:44. Moreover the word here used, signifies "doctrine", and may intend the evangelic doctrine, as it does in Psalm 19:7; which is a psalm concerning the doctrine of the apostles that went into all the world; and in like sense is the word used in Isaiah 2:3; of the doctrine of the Messiah, that is, the Gospel; and is the same with the law, or doctrine of faith, in Romans 3:27. And this may be called the doctrine of the Lord, because he is the author of it; it came by him, he revealed it; and because he is the subject of it; it is concerning him, his person, office, grace, and righteousness; and so far as it was published in the times of David, it was a joyful sound, good news and glad tidings, and the delight of good men;
and in his law doth he meditate day and night; as Joshua was directed to do, and David did, Joshua 1:8. This is to be understood of a diligent reading and serious consideration of it; and of the employment of the thoughts, and of deep study upon it, in order to find out the sense and meaning of it; and which is to be done constantly, every day, as often as there is leisure and opportunity for it; or, as Kimchi on the place observes, whenever a man is free from the business of life; unless this should be taken figuratively, of the day of prosperity and night of adversity, whether in things temporal or spiritual, which are each of them proper seasons to meditate in, upon the word of God and Gospel of Christ.

law--all of God's word then written, especially the books of Moses (compare Psalm 119:1, Psalm 119:55, Psalm 119:97, &c.).

Day and night - Not seldom and slightly, but diligently, and constantly.