Blessed are they that keep his testimonies - His commandments or laws, considered as what he bears witness to concerning that which is just, wise, good. Every law of a parent is to his children a testimony on his part of what is wise and right and good; and so every law of God is his solemn testimony as to what is right and good for man. See Psalm 19:7, note; Psalm 25:10, note.
And that seek him with the whole heart - With a sincere desire to know his will and to do it; without hypocrisy or guile; with no selfish or sinister aims. As God knows the heart, all other modes of "seeking" him must be in vain. It is impossible for man to impose on him by appearances.

Blessed are they that keep his testimonies,.... The whole word of God, the Scriptures of truth, are his testimonies: they testify of the mind of God, and of his love and grace in the method of salvation by Christ; they testify of Christ, his person, offices, and grace; of the sufferings of Christ, and the glory that should follow; and of all the happiness that comes to the people of God thereby. The law is called a testimony, which being put into the ark, that had the name of the ark of the testimony. This is a testimony of the perfections of God, his holiness, justice, and goodness displayed in it; and of his good and perfect will, what should or should not be done. The Gospel is the testimony of Christ, of what he is, has done and suffered for his people, and of the blessings of grace by him; the ordinances of it, baptism and the Lord's supper, testify of the love of God, and grace of Christ; and all these good men keep: they keep the Scriptures as a sacred "depositum"; they hold fast the faithful word of the Gospel, that no man take it from them; and are desirous of observing both the law of God, as in the hands of Christ; and the ordinances of the Gospel, as delivered by him, from a principle of love to him; and such are happy persons in life, at death, and to all eternity;
and that seek him with the whole heart; that is, that seek the Lord by prayer and supplication, with a true heart, and in sincerity; that seek to know more of him, and that in good earnest; that seek for communion and fellowship with him, with the Spirit within them, with all their heart and soul; that seek Christ, and God in Christ, his kingdom, and his righteousness, and that in the first place, early, earnestly, and diligently. The Targum is,
"they seek his doctrine with the whole heart.''

testimonies--The word of God is so called, because in it He testifies for truth and against sin.
seek him--that is, a knowledge of Him, with desire for conformity to His will.