Athanasius... declares that Christ the eternal Son is the “living will” of the Father, and as such His Advent is the advent of the decree, God’s choice, in human flesh. (Peter Leithart)
Is God's election secret or revealed? Both. It's hidden. But hidden in Christ - Matthew 11:25-28:
25At that time Jesus said, "I praise you, Father, Lord of heaven and earth, because you have hidden these things from the wise and learned, and revealed them to little children. 26Yes, Father, for this was your good pleasure.
27"All things have been committed to me by my Father. No one knows the Son except the Father, and no one knows the Father except the Son and those to whom the Son chooses to reveal him.
28"Come to me, all you who are weary and burdened, and I will give you rest.
Christmas is the advent of God's eternal decree - Christ Himself. Lay hold of Him and you lay hold of God's eternal choice.