I will wash mine hands in innocency - The psalmist here refers, as another evidence of his piety, to the fact that it was a ruling purpose of his life to be pure, to worship and serve his Maker in purity. He had stated that he had no sympathy with the wicked, and that he did not make them his companions; he now states what his preferences were, and where his heart was to be found. He had loved, and he still loved the worship of God; he delighted in the pure service of the Most High. Washing the hands is an emblem of purity. So Pilate Matthew 27:24 “took water, and washed his hands before the multitude, saying, I am innocent of the blood of this just person.” Compare Deuteronomy 21:6-7. The word rendered “innocency” means properly “cleanness, purity;” and perhaps the allusion here is to water that is perfectly pure. The sense of the passage is, that he would endeavor to make himself pure, and would thus worship God. He would not come, practicing iniquity, or cherishing sin in his heart. He would banish all from his mind and heart and life that was wrong, and would come with true love to God, and with the spirit of a sincere worshipper.
So will I compass thine altar, O Lord - In this manner, and with this spirit, I will worship thee. The word “compass” may either mean that he would “embrace” it by throwing his arms around it, or that he would “go round” it with others in a solemn procession in worship. The idea is, that he would come to the altar of God with his offering in sincerity and truth. It was to himself one evidence of sincere piety that he so purposed in his heart, or that he was conscious of a desire to worship God in purity and truth. This desire is always an indication of true piety.