Another paradox in Revelation

In the sermon at church on sunday it was pointed out that the following verses contain a significant paradox:

These are the ones coming out of the great tribulation. They have washed their robes and made them white in the blood of the Lamb.

Revelation 7:14

How can you making something white by washing it in blood? This highlights the paradox that through imperfect humans are made perfect in God's sight through the death of Jesus.

Other paradoxes in Revelation concern the Lamb who speaks, the Lamb becomes a shepherd,..