God's Immutability

When we say God is immutable, we mean he does not change. Of course, that's applied to Jesus Christ, the same yesterday, today, forever. But what doesn't change? The eternal Son assumed a human nature. Is that God changing? Theologians have always said, no, that's not what we mean by immutability. Immutability means the attributes of God — again, that "Godness of God" — does not change, so that the eternal Son would assume a human nature does not alter his divine nature. That's what does not change, and so with the Spirit, and so with the Father.