41 We must not indeed pass over the fact that in many manuscripts, both Latin and Greek, nothing is said of the angel's coming or the Bloody Sweat. But while we suspend judgment, whether this is an omission, where it is wanting, or an interpolation, where it is found (for the discordance of the copies leaves the question uncertain), let not the heretics encourage themselves that herein lies a confirmation of His weakness, that He needed the help and comfort of an angel.
Let them remember the Creator of the angels needs not the support of His creatures. Moreover His comforting must be explained in the same way as His sorrow. He was sorrowful for us, that is, on our account; He must also have been comforted for us, that is, on our account. If He sorrowed concerning us, He was comforted concerning us. The object of His comfort is the same as that of His sadness. Nor let any one dare to impute the Sweat to a weakness, for it is contrary to nature to sweat blood. It was no infirmity, for His power reversed the law of nature.
The bloody sweat does not for one moment support the heresy of weakness, while it establishes against the heresy which invents an apparent body, the reality all His body. Since, then, His fear was concerning us, and His prayer on our behalf, we are forced to the conclusion that all this happened on our account, for whom He feared, and for whom He prayed.
Source: On the Trinity (New Advent)