Charles H. Spurgeon on Psalms 26:6

I will wash mine hands in purity. Referring in these words, to the ordinary use of the sacrifices, he makes a distinction between himself and those who professed to offer the same divine worship, and thrust themselves forward in the services of the sanctuary, as if they alone had the sole right to perform them. As David, therefore, and these hypocrites were one in this respect, that they entered the sanctuary, and surrounded the sacred altar together, he proceeds to show that he was a true worshipper, declaring that he not only diligently attended to the external rites, but came to worship God with unfeigned devotion. It is obvious that he alludes to the solemn rite of washing which was practised under the law. He, accordingly, reproves the gross superstition of hypocrites, who, in seeking only the purification of water, neglected true purification; whereas it was God's design, in the appointment of the outward sign, to put men in mind of their inward pollution, and thus to encourage them to repentance. The outward washing alone, instead of profiting hypocrites, kept them at a greater distance from God. When the psalmist, therefore, says, "I will wash my hands in innocence, "he intimates that they only gather more pollution and filth by their washings. The Hebrew word (Nwyqn) nikkayon, signifies the cleanness of anything, and is figuratively used for innocence. We thus see, that as hypocrites derive no moral purity whatever from their washings, David mocks at the labour with which they vainly toil and torment themselves in such rites. John Calvin.