I have rejoiced - I do rejoice; I exult in this; I find my happiness there. The word expresses a high degree of joy.
As much as in all riches - Hebrew, "as upon all wealth." As people rejoice who have great wealth. I find my happiness in religion, as if in the possession of real wealth. Proverbs 10:22.

I have rejoiced -
11. He must consider it his chief happiness to be found in the path of obedience, giving his whole heart and strength to God; and when enabled to do it, he should rejoice more in it than if he had gained thousands of gold and silver. O how great is the treasure of a tender and approving conscience!

I have (c) rejoiced in the way of thy testimonies, as [much as] in all riches.
(c) The prophet does not boast of his virtues, but sets forth an example for others to follow God's word, and leave worldly vanities.

I have rejoiced in the way of thy testimonies,.... The way which the Scriptures, that testify of God and Christ, direct unto; and the principal way is Christ himself, the only way of life and salvation; in which believers walk and go on rejoicing; rejoicing in his person, offices, grace, righteousness, and salvation: the lesser ways the Scriptures point unto are the ways of duty and paths of ordinances; in which truly gracious souls find a great deal of peace, pleasure, and delight;
as much as in all riches; or, "as above all riches" (r): the joy that believers have in the ways of God is superior to that which any natural or worldly man has in his substance of every sort, or be it ever so great; yea, they find such riches in the ways of God, as are vastly preferable to the riches of this world; they find Christ, the pearl of great price, and his unsearchable riches, the riches of grace, and the riches of glory; and even the word of God itself, those testimonies of his, are more desirable than thousands of gold and silver, and give a greater pleasure than the increase of corn and wine.
(r) "sicut super omnibus divitiis", Pagninus; so Junius & Tremellius, Michaelis, Ainsworth.