His vesture (or kingly robe) is dipped in blood, Revelation 19:13 says. Since it is dipped in blood before He actually engages in the battle, this blood cannot, I think, be referring to the blood of His enemies. That leaves then one option: It must be His own blood which He shed upon the cross. His vesture is dipped in His own blood – the blood of battle in which He was engaged many years ago – indicating now that this battle that He fights at the end, like that one, is a battle on behalf of His church. He fights for His bride. He had entered into the fray many years ago upon His cross and He had come out of that battle victorious, though His own blood had been shed upon that cross. He had redeemed His people, purchasing for them righteousness – the righteousness that they now wear as white, clean linen (Revelation 19:14). It is the righteous garments of Jesus Christ's own perfect obedience.
He had defeated sin and Satan upon that cross. He had risen from the dead in victory. And the battle to which He now returns at the end is a battle, then, that He has already won in principle at that cross! That cross is victory! It is glory! That cross is so far from being a moment or emblem of shame to Him! It is His great moment of victory! And so as an army captain would display his colours as he goes into battle, the Lord Jesus Christ, coming in victory upon His white horse, displays the colours of His victory! The red of the blood of His own cross is the colour of the victorious King.1
Cory Griess
13 He is clothed in a robe dipped in blood, and the name by which he is called is The Word of God.