The supreme object of that love is himself

From Redemption Accomplished and Applied:

...propitiation does not detract from the love and mercy of God; it rather enhances the marvel of his love. For it shows thew cost that redemptive love entails. God is love. But the supreme object of that love is himself. And because he loves himself supremely he cannot suffer what belongs to the integrity of his character and glory to be compromised or curtailed. That is the reason for the propitiation. God appeases his own holy wrath in the cross of Christ in order that the purpose of his love to lost men may be accomplished in accordance with and to the vindication of all the perfections that constitute his glory. (32)