Luke 9:33

(non occ.) Peter also was ignorant what he said, seeing that it was not proper to make three tabernacles for the three. For the servants are not received with their Lord, the creature is not placed beside the Creator.

But Peter distinguished not only by earnest feeling, but also by devout deeds, wishing like a zealous workman to build three tabernacles, offers the service of their united labour; for it follows, Let us make three tabernacles, one for thee, &c. Nor does the condition of man in this corruptible body allow of making a tabernacle to God, whether in the soul or in the body, or in any other place; and although he knew not what he said, yet a service was offered which not by any deliberate forwardness, but its premature devotion, receives in abundance the fruits of piety. For his ignorance was part of his condition, his offer of devotion.

(de Con. Ev. l. ii. c. 56.) Now in what Luke here says of Moses and Elias, And it came to pass as they departed from him, Peter said unto Jesus, Master, it is good for us to be here, he must not be thought contrary to Matthew and Mark, who have so connected Peter's suggestion of this, as if Moses and Elias were still speaking with our Lord. For they did not expressly state that Peter said it then, but rather were silent about what Luke added, that as they departed, Peter suggested this to our Lord.

For perhaps holy Peter imagined that the kingdom of heaven was at hand, and therefore it seemed good to him to abide on the mount. He knew not what he said, for neither was the time come for the end of the world, or for the Saints' enjoyment of their promised hope. And when the dispensation was now commencing, how was it fitting that Christ should abandon His love of the world, Who was willing to suffer for it?

(Orat. de Trans. fig.) It were not good for thee, Peter, that Christ should abide there, for if He had remained, the promise made to thee would never receive its accomplishment. For neither wouldest thou have obtained the keys of the kingdom, nor the tyranny of death been abolished. Seek not bliss before its time, as Adam did to be made a God. The time shall come when thou shalt enjoy the sight without ceasing, and dwell together with Him who is light and life. (ubi sup.) But the Lord ordained thee not the builder of tabernacles, but of the universal Church. Thy words have been brought to pass by thy disciples, by thy sheep, in building a tabernacle, not only for Christ, but also for His servants. But Peter said not this deliberately, but through the inspiration of the Spirit revealing things to come, as it follows, not knowing what he said. (ubi sup.) It behoved Him also not to confine the fruit of His incarnation to the service of those only who were on the mount, but to extend it to all believers, which was to be accomplished by His cross and passion.