Adam Clarke on Psalms 119:1

Blessed are the undefiled in the way - אשרי תמימי דרך ashrey temimey darech, "O the blessedness of the perfect ones in the way." This Psalm begins something like the first, where see the notes Psa 1:1-6 (note). By the perfect, which is the proper meaning of the original word, we are to undertsand those who sincerely believe what God has spoken, religiously observe all the rules and ceremonies of his religion, and have their lives and hearts regulated by the spirit of love, fear, and obedience. This is farther stated in the second verse.