God planted a vision for missions in Don's eight-year-old heart when a Navajo Christian visited his family and the church his father pastored. Much later, after Bible college and a two-year pastorate, Don and his wife, Donna, left their families and New York home for the Navajo Reservation in Arizona. Despite minimal support and no training in culture or language, they were confident in the Lord's leading and stepped out in faith. They joined Navajo Bible School and Mission to disciple believers and incorporate a Navajo church in Fort Defiance.

Having observed detrimental mission and governmental practices causing and perpetuating a welfare mentality and dependency among the Natives, Don determined, with the Lord's help, to develop a truly indigenous church with indigenous leadership, indigenous support, and indigenous outreach. While serving at Navajo Bible Church, he realized that the Navajo Reservation was becoming saturated with missions while some other tribes had no church-planting efforts. Opportunities soon arose for him and Donna and two other couples to reach beyond Navajos to Havasupais and Hualapais. Under the Lord's leading, the three couples founded United Indian Missions (UIM) in 1956 on the same indigenous principles by which Navajo Bible Church had been organized.

Serving through the years as UIM's U.S. Field Director, Assistant Director, General Director, and Director Emeritus, Don rejoiced to see the Lord expand UIM to Mexicans, Hispanics, and indigenous peoples in Canada, the U.S., and Mexico. He challenged young and old alike to be involved in the Lord's work. "Every believer ought to be active in some aspect of the Lord's work . . .," he declared. "If we're faithful where God has us now, He will make it clear . . . if He wants us somewhere else." For him, the most rewarding aspects of ministry were seeing people come to Christ and working alongside Native Christian leaders. He was ever grateful for Donna's indispensable role in their family and ministry. Don received an honorary Doctor of Divinity degree from Native people at Baptist Theological Seminary in Guaymas, Sonora, Mexico, in 1995 and the "Faithful Servant Award" from Independent Fundamental Churches of America in 2012--both fitting honors for one who walked by faith.

At Don's memorial service Native believers affirmed Don's impact. "Mr. Fredericks was truly an ambassador of Jesus Christ to our Native people," one said. Navajo pastor and UIM board member Mike Calvin recalled a time Don addressed the Southwestern School of Missions (now Indian Bible College) student body. "He challenged us from 2 Timothy, telling us to study to show ourselves approved unto God, to correctly handle the word of truth, and to preach the Word in season and out of season. He encouraged us to look beyond our tribe and our reservation to a world in need of Jesus. Throughout the years he always encouraged Native men to become leaders and believers to remain faithful. He exemplified love, faith, and patient hope, the cardinal virtues of the Christian life."

Don's faithfulness to the Lord will continue to impact positively those who knew him.