In John’s gospel, Jesus famously says “I am” again and again. These allude to the Old Testament’s revelation of “I am,” but if we can press the wording, they are also statements about the being of Jesus. Let’s say they are ontological statements.
The predicate, though, describes Jesus’ ministry in the world. Jesus does not say, “I am infinite, eternal, and unchangeable in My being, power, holiness, goodness, and truth” (though He could have). He says “I am Bread” and “I am light” and “I am the good shepherd.”
But then how can these be ontological statements about who or what Jesus is . Perhaps we need to loosen the ontological claim: Jesus is no more eternally and inherently bread than He is eternally and inherently flesh; He becomes bread. That solution breaks the link with the Old Testament revelation of Yahweh. Alternatively, we could say that Jesus the Son is inherently and eternally bread, light, shepherd - but then His being seems to be dependent on creation. If He is bread for the world, He ceases to be God.
Neither of these solutions satisfies. This is the riddle that Barth strove to answer with his meditations on election and on “God for us.” Whether we follow Barth in every respect, he was entirely right in his insistence that the Triune God is free to be God for us, that He is God-for-us without ceasing to be antecedently God in Himself.