How were the high priest's cleansing preparations like the Passover lamb's perfection?
The high priest's cleansing ritual paralleled the Passover lamb's required perfection. As the Passover lamb had to be perfect and without blemish, so the high priest had to complete the whole ritual of cleansing before entering the holy place on the Day of Atonement.
Les explains that the Day of Atonement involved preparations the priest had to go through. He points out the analogy: even as the Passover lamb had to be perfect without blemish, so also this high priest had to go through the whole ritual of cleansing. This was necessary because the Old Testament believer could not go into God's presence, since sins were only covered, not atoned, and the high priest could enter behind the veil only once a year. These pictures were fulfilled when Christ went to the cross on our behalf.