And we must observe, that, as when the Lord was baptized in Jordan, so on the mountain, covered with brightness, the whole mystery of the Holy Trinity is declared, because we shall see in the resurrection that glory of the Trinity which we believers confess in baptism, and shall praise it all together.
Nor is it without reason that the Holy Ghost appeared here in a bright cloud, there in the form of a dove; because he who now with a simple heart keeps the faith which he hath embraced, shall then contemplate what he had believed with the brightness of open vision. But when the voice had been heard over the Son, He was found Himself alone, because when He shall have manifested Himself to His elect, God shall be all in all, yea Christ with His own, as the Head with the body, shall shine through all things. [1 Cor 15:28]
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).