"Even the prophets who were favored with the special illumination of the Spirit did not fully comprehend the import of the revelations committed to them. The meaning was to be unfolded from age to age, as the people of God should need the instruction therein contained. GC 344.1"
"Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you:"
Both passages discuss the incomplete understanding of prophecy at the time it was given, and the gradual unfolding of its meaning over time.
"Peter, writing of the salvation brought to light through the gospel, says: Of this salvation “the prophets have inquired and searched diligently, who prophesied of the grace that should come unto you: searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow. Unto whom it was revealed, that not unto themselves, but unto us they did minister.” 1 Peter 1:10-12 . GC 344.2"
"Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace that should come unto you: Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow. Unto whom it was revealed, that not unto themselves, but unto us they did minister the things, which are now reported unto you by them that have preached the gospel unto you with the Holy Ghost sent down from heaven; which things the angels desire to look into."
Ellen White directly references 1 Peter 1:10-12 in this passage.
"Yet while it was not given to the prophets to understand fully the things revealed to them, they earnestly sought to obtain all the light which God had been pleased to make manifest. They “inquired and searched diligently,” “searching what, or what manner of time the Spirit of Christ which was in them did signify.” What a lesson to the people of God in the Christian age, for whose benefit these prophecies were given to His servants! “Unto whom it was revealed, that not unto themselves, but unto us they did minister.” Witness those holy men of God as they “inquired and searched diligently” concerning revelations given them for generations that were yet unborn. Contrast their holy zeal with the listless unconcern with which the favored ones of later ages treat this gift of Heaven. What a rebuke to the ease-loving, world-loving indifference which is content to declare that the prophecies cannot be understood! GC 344.3"
"Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow."
EGW directly quotes 1 Peter 1:11 and builds her argument around it, emphasizing the diligence of the prophets in understanding the prophecies.
"Though the finite minds of men are inadequate to enter into the counsels of the Infinite One, or to understand fully the working out of His purposes, yet often it is because of some error or neglect on their own part that they so dimly comprehend the messages of Heaven. Not infrequently the minds of the people, and even of God's servants, are so blinded by human opinions, the traditions and false teaching of men, that they are able only partially to grasp the great things which He has revealed in His word. Thus it was with the disciples of Christ, even when the Saviour was with them in person. Their minds had become imbued with the popular conception of the Messiah as a temporal prince, who was to exalt Israel to the throne of the universal empire, and they could not understand the meaning of His words foretelling His sufferings and death. GC 344.4"
"For my thoughts are not your thoughts, neither are your ways my ways, saith the Lord. For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts."
Both passages address the limitations of human understanding in comprehending God's plans and messages. EGW uses the example of the disciples' misunderstanding of Jesus's mission to illustrate this point, while Isaiah 55:8-9 provides the foundational principle.