No One Has Seen God
This statement does not contradict OT theophanies. Moses, Isaiah, and Ezekiel had visionary encounters — but no one has seen God in His full divine essence. Even Moses saw only God's "back" (Exodus 33:23). The infinite God cannot be directly apprehended by finite human sight.
The Only Begotten Son in the Father's Bosom
To be "in the bosom" is to be in the position of intimate relationship — like the beloved disciple at the Last Supper (John 13:23). The Son has complete, eternal, interior knowledge of the Father. He is not an observer of God but a participant in the divine life.
He Has Declared — Exegeted — Him
"Declared" (Greek: exegesato) is the root of exegesis. Jesus is the exegesis of God — He unpacks who God is from the inside. Every action, word, and attitude of Jesus is a commentary on the invisible Father. To see Jesus is to see God (John 14:9).
Applications for Today
If you want to know what God is like — look at Jesus. His compassion for the sick is God's compassion. His anger at hypocrisy is God's anger. His welcome of sinners is God's welcome. Jesus is God in human form, fully legible to human eyes.