Ablution (or washing), was practiced in the following ways in the Bible:
When a person was initiated into a higher state: e.g., when Aaron and his sons were set apart to the priest’s office, they were washed with water previous to their investiture with the priestly robes (Leviticus 8:6).
Before the priests approached the altar of God, they were required, on pain of death, to wash their hands and their feet to cleanse them from the soil of common life (Exodus 30:17-21). To this practice the Psalmist alludes, Psalm 26:6.
There were washings prescribed for the purpose of cleansing from positive defilement contracted by particular acts. Of such washings eleven different species are prescribed in the Levitical law (Leviticus 12-15).
A fourth class of ablutions is mentioned, by which a person purified or absolved himself from the guilt of some particular act. For example, the elders of the nearest village where some murder was committed were required, when the murderer was unknown, to wash their hands over the expiatory heifer which was beheaded, and in doing so to say, “Our hands have not shed this blood, neither have our eyes seen it” (Deuteronomy 21:1-9).
So also Pilate declared himself innocent of the blood of Jesus by washing his hands (Matthew 27:24). This act of Pilate may not, however, have been borrowed from the custom of the Jews. The same practice was common among the Greeks and Romans.
The Pharisees carried the practice of ablution to great excess, thereby claiming extraordinary purity (Matthew 23:25). Mark (7:1-5) refers to the ceremonial ablutions. The Pharisees washed their hands “oft,” more correctly, “with the fist” (Revised King James Version, “diligently”), or as an old father, Theophylact, explains it, “up to the elbow.” (Compare also Mark 7:4; Leviticus 6:28; 11:32-36; 15:22).
Christ washes confessed repentant believers of their sins.