I thought about it for a long time and prayed about it and searched all the scriptures in the epistles relating to it. I was already aware of that verse and understand what you mean. But besides the words we have in the Bible on it, we also have pictures to show us.
In Exodus, the people of God applied the blood to their house on the top and sides of their door poat in the pattern of the cross, signifying the blood of the cross. Then after that, they were led through the Red Sea, which signifies baptism, where the Egyptians were swept away by the waters of the Red Sea, just like our sins are washed away in baptism.
So these are two separate events where blood and water are applied. The blood was applied before they went through the Red Sea.
The blood, water, and Spirit are three witnesses, and each one has it's own place. If not, then repentance wouldn't have any witness, and wouldn't have any effect or benefit, including forgiveness, because God is not going to forgive sin and just leave it uncovered.
Here's a key scripture in the epistles in words "Blessed are they whose iniquities are forgiven, and whose sins are covered".
Romans 4:7.
So our sins can be covered and not be washed away. So these are two separate events. The blood being applied in repentance, where our sins are covered. And water applied in baptism, where blood and water bear witness with each other as two witnesses (the minimum by law), and then our sins are washed away.
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