'Unfasten' in the Bible

John answered them all by saying, “As for me, I baptize you [only] with water; but One who is mightier [more powerful, more noble] than I is coming, and I am not fit to untie the strap of His sandals [even as His slave]. He will baptize you [who truly repent] with the Holy Spirit and [you who remain unrepentant] with fire.