Charles H. Spurgeon on Psalms 89:18

For the Lord is our defence. Whoever else may defend us, he is our ultimate Defender and Shield. And the Holy one of Israel is our king. He who protects should govern, our defender should be acknowledged as our king. Kings are called the shields of nations, and the God of Israel is both our Ruler and our Defence. Another sense may be that Israel's defender and king was of the Lord, belonging to him and sent by him; even the protectors of the land being themselves protected by the Lord. The title "the Holy One of Israel" is peculiarly delightful to the renewed heart. God is one, we worship none beside. He is holiness itself, the only being who can be called "the Holy One", and in his perfection of character we see the most excellent reason for our faith. He who is holy cannot break his promises, or act unjustly concerning his oath and covenant. Moreover, he is the Holy One of Israel, being specially the God of his own elect, ours by peculiar ties, ours for ever and ever. Who among the saints will not rejoice in the God of election? Are they not indeed a people greatly blessed who can call this God their God for ever and ever?