In one sense, to say that Jesus “expounded all scriptures in one” may mean that our Lord taught the people the entire plan of salvation out of the scriptures, perhaps even opening the heavens and providing the visions necessary to understand what had been, what was, and what was to come.
Such a panoramic vision might not be unlike what was vouchsafed to Enoch (Moses 7), Moses (Moses 1), Nephi (1 Nephi 13-14), the brother of Jared (Ether 3), or Joseph Smith (D&C 76). Of his own experience in vision, Joseph Smith said:
“Nothing could be more pleasing to the Saints upon the order of the Kingdom of the Lord, than the light which burst upon the world through the ... vision [D&C 76]. Every law, every commandment, every promise, every truth, and every point touching the destiny of man, from Genesis to Revelation, where the purity of the Scriptures remains unsullied by the folly of men, go to show the perfection of the theory (of different degrees of glory in the future life) and witness the fact that the document is a transcript from the records of the eternal world.” (Teachings, p. 11.)
On a later occasion, the Prophet explained:
“I could explain a hundred fold more than I ever have of the glories of the kingdoms manifested to me in the vision, were I permitted, and were the people prepared to receive them’ (Teachings, p. 305).”