Do you need a bath? Or do you just need your feet washed? (John 13:8-10).
I used to work as a biochemist and in the lab we were always very concerned to use pure chemical solutions for our experiments because even trace amounts of contaminants could ruin an experiment, rendering the results useless. Yet none of our chemicals were ever 100% pure, even the ‘ultrapure’ water was not absolutely pure because it absorbed contaminants from the equipment used to purify it, the atmosphere, and even the glass in which it was stored - at best it was relatively pure.
God alone is absolutely pure, so pure that he cannot even look upon evil (Habakkuk 1:13). Which leaves us with a problem — we have deceitful, sinful hearts and God is so pure that sin cannot exist in His presence. We need to be made clean, and not just relatively clean, absolutely clean. The One who washed Peter is the only way for any of us to be cleansed so that we can stand before God who is holy.