But about that day or hour no one knows, not even the angels in heaven, nor the Son, but only the Father.
The scandal of the passage for orthodox trinitarians is familiar; but one of the simplest responses is to read it as a part of a larger whole that is given fully in Christ’s last revelation:
It is not for you to know times or epochs which the Father has fixed by His own authority; but you will receive power when the Holy Spirit has come upon you; and you shall be My witnesses both in Jerusalem, and in all Judea and Samaria, and even to the remotest part of the earth.
Acts 1: 7-9
While the operations of the Trinity in creation are indistinguishable (otherwise we would not need revelation to know them) their operations in salvation history are not; and so the Son does not know the time of the final revelation because to set this is the work of the Father. The Father thus constructs the formal structure of times which break forth in revelation, Christ is the one revealed (“you shall be my witnesses”), and the Spirit is the one whose power effects the revelation (“You will receive power when the Holy Spirit, etc.”). Christ no more knows the hour of salvation than, say, the Spirit knows the message that is revealed, which is not far from how he is actually spoken of:
When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come. He will glorify me, for he will take what is mine and declare it to you. All that the Father has is mine; therefore I said that he will take what is mine and declare it to you.
In other words, the “knows not” language is a way of speaking of the order among the distinct work of the trinitarian persons in the work of salvation history. If we wanted to describe the equality of the persons in this work we would have to give a different but complementary description – perhaps one that appropriates St. Thomas’s metaphor of the flower, i.e. The work of the Father is to set the conditions that of themselves bring forth the flower, the Holy Spirit is the energy of the flowering, and the Son is the flower itself. More simply, we could point out that to effect salvation or be the final revelation is proper to God alone.