Psalm 89:18 For the LORD is our defence; and the Holy One of Israel is our king.

Who is the "Holy One"? When the demon Legion (Mark 1:24) saw Jesus, they called him "the Holy One of God". When the people rejected Jesus, Acts 3:14 says they denied "the Holy One". So Jesus is the Holy One, the King of Jerusalem.

But..... Habakkuk 1:12 Are You not from everlasting, *O LORD my God, my Holy One*? .....

So the LORD i.e. - Yahweh/ Jehovah is "the Holy One". Scripture says "the Holy One" not the Holy two, Jesus is the revealed name of the Holy One, who is God Almighty, the Everlasting God of Habakkuk 1:12, the Eternal Father of Isa 9:6.

Therefore, when the Psalmist said: the LORD is our defence and the Holy one is our King, both are a reference to Jesus. He is king of Jerusalem (his people), and a king will defend his city. When we put our trust in him, we are trusting in the Omnipotent God to protect us and who can do the job better than him? Selah!