After taking notice of this lack of knowledge in a person, who, on the strength of his magisterial station, set himself above others, and blaming the unbelief of such men, our Lord says, that if such as these do not believe, others will: No one hath ascended into heaven, but He that came down from heaven, even the Son of man who is in heaven. This may be rendered: The spiritual birth shall be of such sort, as that men from being earthly shall become heavenly: which will not be possible, except they are made members of Me; so that he who ascends, becomes one with Him who descended. Our Lord accounts His body, i. e. His Church, as Himself.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: De Pecc. mer. et remiss. c. xxxi