Yet this is not the whole truth of the matter. We do assert that God, that is, the whole Godhead, is one person…. In other words, we are bound to maintain the identity of the attributes of God with the being of God in order to avoid the specter of brute fact.”
…Over against all other beings, that is over against created beings, we must therefore hold that God’s being presents an absolute numerical identity. And even within the ontological Trinity we must maintain that God is numerically one. He is one person. We say that we believe in a personal God we do not merely mean that we believe in a God to whom the adjective “personality” may be attached. God is not an essence that has personality; He is absolute personality. Yet, within the being of the one person we are permitted and compelled by Scripture to make the distinction between a specific or generic type of being, and three personal subsistences.
Cornelius Van Til, An Introduction to Systematic Theology (1971).