When Assemblies of God U.S. missionary Santiago Guerrero conducts church seminars about aberrant religious groups, it’s more than theoretical. He has firsthand knowledge.

As a teenager and young adult, Guerrero spent many evenings and Saturdays knocking on doors, spreading the beliefs of Jehovah’s Witnesses.

The Corpus Christi, Texas, native joined the Jehovah’s Witnesses at age 12 after a neighborhood friend invited him to attend a meeting at the local Kingdom Hall gathering place.

“Jehovah’s Witnesses seemed to have the answers to all of life’s problems,” recalls Guerrero, now 54. “All the people were so dedicated to the cause. I thought they must have the truth.”

As he grew, Guerrero became an ardent disciple and began espousing the doctrines himself. Like his mentors, he believed the Jehovah’s Witnesses were the only representatives of God’s church on earth and the only ones who would receive salvation.

Guerrero eventually became an editor at The Watchtower, the group’s flagship publication.

Many churchgoers are wary of answering the door when Jehovah’s Witnesses come around. But Guerrero found it baffling that self-proclaimed Christians were unwilling to talk about their faith.

Some who did interact with him had trouble answering basic questions about their beliefs. Time and again, such people accepted Guerrero’s Kingdom Hall invitation and converted.

When Guerrero was 25, a well-educated Christian co-worker started engaging him in spiritual conversations. After six months of verbal exchanges about the Bible, Guerrero surrendered his life to Christ.

Guerrero soon enrolled at Instituto Biblico Magdiel, an Assemblies of God Bible college in Matamoros, Mexico. (Guerrero’s grandmother attended an AG Spanish-language church in Robstown, Texas.)

After graduating in 1998, Guerrero began ministering to Hispanic workers at pork processing plants in the Northern Missouri Assemblies of God district, often challenging the teachings of Jehovah’s Witnesses and The Church of Jesus Christ of Latter-day Saints (Mormons).

By 2000, Guerrero had become a full-time AG U.S. missionary with Intercultural Ministries. His ministry, Counter-Cult Mission, is based in Kansas City, Missouri.

Jehovah’s Witnesses and Mormons — two faiths that emphasize door-to-door evangelism — have a combined 8 million U.S. adherents.

Globally, Mormons have more than 17 million members and 100,000 missionaries. According to Guerrero, many Mormons at one time attended an evangelical church.

Guerrero spends most weekends traveling to churches conducting weekend seminars. He frequently leads sessions on Saturday and teaches during the Sunday service.

“My hope is that Christians will not only defend their faith, but that they share their faith when they get a knock on the door.”
— Santiago Guerrero

“My work is to equip local churches on what these groups believe,” Guerrero says. “My hope is that Christians will not only defend their faith, but that they share their faith when they get a knock on the door.”

Guerrero teaches Christians to recognize cult characteristics, such as service commitments as a means of salvation and reliance on extrabiblical authority. The LDS Church, for example, holds that the Book of Mormon has supremacy over the Bible where passages conflict.

“My goal is that the Christian not be deceived,” Guerrero says. “We need to let them know why we’re Christian.”

He says Christians often feel overwhelmed when talking with Mormons and Jehovah’s Witnesses. Many don’t know the basic teachings of these groups or understand how they differ from biblical Christianity.

Adding to the confusion, Mormons and Jehovah’s Witnesses use familiar terminology in unfamiliar ways. For example, Mormons might talk at length about Jesus, but with an understanding that is miles apart from evangelicals.

Followers of aberrant religious groups don’t have the assurance of salvation, Guerrero stresses.

“They think they must work their whole life for salvation,” he says. “They don’t realize they can have it today.”

According to Guerrero, Christians who interact with Jehovah’s Witnesses often get caught up in secondary issues, such as the group’s avoidance of Christmas celebrations or refusal to salute the American flag.

“Salvation must be the main issue,” Guerrero says. “Like the Philippian jailer and the apostle Paul, the most important question is, ‘What must I do to be saved?’” (Acts 16:30).

Hope Church in Wichita, Kansas, has invited Guerrero to speak three times at question-and-answer forums since Bobby Massey became senior pastor in 2014.

Massey previously utilized Guerrero’s seminars during his 29 years at LifePoint Church in Valley Center, Kansas. An LDS temple is being built between Wichita and Valley Center. Another is slated for construction just south of Springfield, Missouri, national headquarters of the U.S. Assemblies of God.

“Santiago equips people about how to be relationally involved with those in cults,” Massey says. “The tendency is to repel those who come to your door, but he teaches how to get to know them and interact with them.”

Massey says Guerrero has been a catalyst for confronting false doctrine.

“Santiago has a deep desire to equip the people of God according to the Word,” Massey says. “And without being arrogant, he brings the truth in love to those who have been deceived.”

Typically, Guerrero has five ongoing Bible studies with Mormons and Jehovah’s Witnesses. Rarely a day goes by that he isn’t sharing the gospel with them.

When members of tight-knit LDS or Jehovah’s Witnesses groups leave, they often experience shunning from friends and relatives. Guerrero helps them find welcoming, Bible-believing church communities.

“People don’t convert to Mormonism because of doctrine,” Guerrero says. “It’s because they are helped in a time of need.”

Although he grew up in a non-Christian home, Guerrero has seen several members of his own family come to Christ. His mother, Maria Piña, is now a pastor in Robstown, Texas. His brother Oscar pastors Isglesia Emanuel Asambleas de Dios in Provo, Utah — the epicenter of Mormonism.

Guerrero and his wife, Margarita — whom he met in Bible college — have three grown children, Thelma, Melanie, and Santiago III.

This article appears in the Spring 2025 issue of Influence magazine.