Albert Barnes Commentary Psalms 119:111

"Thy testimonies have I taken as a heritage for ever; For they are the rejoicing of my heart." — Psalms 119:111 (ASV)

Your testimonies - Your law; your revealed will; the revelation which you have given considered as your solemn “testimony” as to what is true and right.

Have I taken as a heritage forever - As my inheritance; as my property; as that which I consider to be of real and permanent value. The Hebrew word used here - נחל nachal - means to receive as a possession; to acquire; to possess as wealth; and then, to inherit. It is usually applied to the possession of the promised land as an inheritance. Here it means that the law of God was to him as such a possession. He regarded it as one does a rich inheritance. He chose it as his portion above all else.

For they are the rejoicing of my heart - My happiness is in them. I find constant comfort in them. See Psalms 119:77, Psalms 119:92. Compare the notes at Psalms 1:2.