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Kristin Murphy, Deseret News
As he leaves the Conference Center podium, President Thomas S. Monson shakes hands with Sisters Linda K. Burton and Emri Elizabeth Smith, who offered the opening prayer in the General Women's Meeting on Saturday, March 29, 2014. Behind him are his counselors, President Henry B. Eyring and President Dieter F. UIchtdorf.

SALT LAKE CITY — Few decisions have electrified the LDS Church like President Thomas S. Monson's dramatic announcement during the faith's October 2012 general conference that women could serve missions as early as age 19 and men at 18.

Before he was done speaking, suddenly eligible Mormon teens immediately began to text their bishops with requests for interviews, the first step in a missionary application. By that night, lines formed outside of some bishops' offices. Within days, the number of missionary applications had soared 471 percent. Within a year, the overall number of missionaries jumped from 58,000 to more than 83,000.

The missionary age-change decision especially galvanized young Mormon women, who previously could not serve until age 21. In the first year after President Monson's announcement, the number of sister missionaries skyrocketed from 8,055 to nearly 21,673. Women became 26 percent of the church's missionary force, up from 12 percent.

The phenomenon spurred The New York Times to observe that "the standard image of a Mormon missionary, a gangly young man in a dark suit, was suddenly out of date."

That dynamic has altered The Church of Jesus Christ of Latter-day Saints forever, say Mormons and Mormon scholars, making the change in missionary age — especially for young women — one of the prominent pillars of President Monson's eight-year administration as the faith's prophet and president.

"I think the No. 1 thing he'll be remembered for by most of the church is the age-change policy for missions," said Patrick Mason, who fills the Howard W. Hunter Chair of Mormon Studies at Claremont Graduate University. "That had a dramatic influence on so many individual lives and families, and it meant drastically higher numbers of women were going into the mission field than ever before. I think we're going to look back on that as really a game-changer for the church in a lot of different ways."

President Monson also oversaw a raft of additional moves that increased the visibility and voice of women in the church, as well as successful advertising and social media campaigns that reached tens of millions around the world. He left a lasting imprint on church leadership by calling five new members to the Quorum of the Twelve Apostles.

Like some other LDS Church presidents before him, President Monson's advanced age began to affect his ministry by 2014 or 2015. At the October 2015 general conference, President Monson noticeably weakened during his talk.

Two months later, one of his two counselors, President Dieter F. Uchtdorf, said the church president was experiencing issues with his short-term memory and struggling with long work days. He no longer was able to work every day.

In May 2017, the church released a statement saying: "Because of limitations incident to his age, President Monson is no longer attending meetings at the church offices on a regular basis. He communicates and confers with his counselors on matters as needed."

President Monson had spoken briefly twice in the April 2017 general conference, but had been hospitalized briefly the day following the conference's conclusion.

He did not attend the October 2017 general conferece, continuing to deal with limitations related to advanced age. It was the first time in more than 20 years that the LDS Church president didn't speak, preside or be present for at least one of the church's biannual general conference session.

Mason, the Claremont scholar, said President Monson continued and grew many of the outreach initiatives of his predecessor, President Gordon B. Hinckley. One example is the "I'm a Mormon" campaign launched in 2008, soon after President Monson succeeded President Hinckley. Today, there are more than 400,000 "I'm a Mormon" profiles online, a significant number for a church with 15.6 million members, up from 13.5 million at the start of the Monson administration.

The church launched new social media campaigns at Easter and Christmas beginning in 2014. The 2015 Easter video "Because He Lives" generated 29.6 million views, with 21 million outside the United States. The church bought YouTube's banner ad in nine countries that day, and 329 million people who visited the website's home page on Easter saw at least part of a 15-second clip of the video.

That illustrated a social media strategy that grew to include popular Face to Face events on Facebook and YouTube for church youths and young single adults with LDS leaders and celebrities.

A revolution in church teaching continued, with the start of the "Come, Follow Me" curriculum for teenagers in 2013 and the launch in 2016 of the new guide for church teachers — "Teaching in the Savior's Way" — and monthly teacher council meetings in each congregation.

One of President Monson's favorite activities was dedicating new temples. He delighted in interacting with LDS children around the world at cornerstone ceremonies. He dedicated a number of the 35 new temples completed during his presidency, beginning with the faith's 125th sacred edifice in 2008 and ending in last month with the 159th, the Cedar City Utah Temple.

President Monson drew audible gasps from the Conference Center congregation during general conference when in he announced in 2012 the mission-age change, in 2011 that the church would rebuild the burned-out Provo Tabernacle as the Provo City Center Temple, and in 2008 when he announced the Rome Italy Temple.

His administration was a noteworthy era for transparency. His First Presidency approved and published online 12 Gospel Topics essays on issues in church history and doctrine that provided new insights and official statements on issues from race and the priesthood to Heavenly Mother. Mason and other scholars said the essays weren't perfect but lauded them for their scholarly presentation and as a major step forward for the faith.

Though President Monson is now gone, his impact on the Quorum of the Twelve will be felt for what could be decades. He called five men to the quorum during his tenure — Elders D. Todd Christofferson, Neil L. Andersen, Ronald A. Rasband, Gary E. Stevenson and Dale G. Renlund. President Monson also called all seven men now serving in the presidency of the Seventy, a group that may include future apostles.

Many of the accomplishments of his administration will be lasting, but it was the mission age change and other moves made to increase the role and visibility of women in the church that might have the broadest and most memorable impact.

Under President Monson's leadership, the church expanded the role of the wives of mission presidents and created a new position for women serving missions — sister training leader. Women leaders now regularly give prayers at the church's general conferences, during which they also sit in the center of the stand, and the women's session has become an official part of general conference.

In 2015, the church added the women who lead the faith's worldwide organizations for women, teenage girls and children to the church's key, leading executive councils. Those women's leaders travel the world, training local priesthood leaders and ministering to members of all ages.

On a local level, the church placed increased emphasis on contributions by women, who are members of every local ward and stake council.

The mission-age change was prophetic and already has begun to strengthen women and girls in the church and their families, said Sister Elaine Dalton, who served as the church's general Young Women president from 2008 to 2013.

"This one announcement is like throwing a stone in a pond — the ripple effects emanate out and encircle the world," she said. "We now have a generation of women who return from their missions with enhanced study and teaching skills who are seeking to complete their college education, who are growing in truth and righteousness, marrying in the temple and teaching their children the doctrines that will help them to navigate an increasingly challenging season in the history of the world."