That led to the Utah-based faith's new policy regarding same-sex Mormon couples that they would be labeled "apostates" and that their children would not be allowed baptism and other LDS religious rites until they turn 18.
"Each of us during that sacred moment felt a spiritual confirmation," Nelson, next in line for the Mormon presidency, told the faith's young adults in the first official explanation of the hotly debated policy's origins. "It was our privilege as apostles to sustain what had been revealed to President Monson."
Nelson explained that revelation from the Lord to his servants is a sacred process.
"The [three-member] First Presidency and Quorum of the Twelve Apostles counsel together and share all the Lord has directed us to understand and to feel, individually and collectively," he said. "And then, we watch the Lord move upon the president of the church to proclaim the Lord's will."
He said that protocol was followed when Monson, in 2012, announced lower minimum ages for full-time Mormon missionary service and again late last year with the new policy on same-sex couples and their children.
The 91-year-old apostle, joined by his wife, Wendy Watson Nelson, spoke from the campus of church-owned Brigham Young University-Hawaii, and his remarks were beamed across the globe and live-streamed on the Internet.
Nelson's talk addressed "millennials" those born between the early 1980s and the early 2000s about their goals, their worries and their strengths.
These young adults were sent "to Earth during the most compelling dispensation in the history of this world," the apostle said, " … to help prepare the people of this world for the Second Coming of Jesus Christ and his millennial reign."
This is civilization's "eleventh hour," Nelson said. "The Lord has declared that this is the last time he will call laborers into his vineyard to gather the elect from the four quarters of the Earth."
Millennials will be challenged and tested as the biblical Abraham, who was asked to ritually sacrifice his son. They will have to defend the faith from critics and stay true to their beliefs.
Young Mormons, like all members, should seek God in prayer for their own answers and confirmations about these issues, he said. "Every one of us has questions. Seeking to learn, understand and recognize truth is a vital part of our mortal experience. … You, too, will learn best by asking inspired questions."
The safest course, Nelson advised, is to heed the words of Mormon leaders, particularly Monson.
"Prophets see ahead. They see the harrowing dangers the adversary has placed, or will yet place, in our path," Nelson said. "Prophets also foresee the grand possibilities and privileges awaiting those who listen with the intent to obey.
" ... You may not always understand every declaration of a living prophet," he added. "But when you know a prophet is a prophet, you can approach the Lord in humility and faith and ask for your own witness about whatever his prophet has proclaimed."
Nelson, who became president of the Quorum of the Twelve Apostles last year, warned his listeners to beware of those who might tear down their faith.
"The somber reality is that there are 'servants of Satan' embedded throughout society," he said. "So be very careful about whose counsel you follow."
In the end, the apostle reminded the young people that they were born for this time with an important assignment: to usher in the Second Coming of Jesus Christ.