Last summer, Schaap, 55, was fired from First Baptist Church of Hammond, the 40,000-member congregation of which he had led for 11 years. Upon his firing, Schaap admitted that he had a sexual relationship with the young member of his church.
In court Wednesday, U.S. District Judge Rudy Lozano told Schaap the sex crimes were serious in that they were "dealing with the treasures that are most important to us - our children," the Northwest Indiana Times reports.
The 12-year prison sentence for Schaap was two years longer than the sentence recommended by prosecutors, according to Reuters, and also includes five years of supervised release.
According to letters released by federal prosecutors last week as part of the government's sentencing memorandum, Schaap wrote to the teen that his sexual relationship with her was "exactly what Christ desires for us. He wants to marry us + become eternal lovers!”
Schaap reportedly "groomed" the girl through counseling sessions and had sex with her many times -- including during trips to a Michigan cabin, a Crete, Ill. vacation home and in his office during a youth conference, according to Chicago magazine, which ran a detailed feature on the pastor last year. Schaap also reportedly texted the girl often -- as many as 662 times in one month.
In letters written to the court, the girl said the former pastor "told me to confide in him, to trust him, and he made me feel safe and comfortable around him as a man of God. … (Schaap) preyed on that trust and my vulnerability," the Chicago Sun-Times reports.
Schaap's inappropriate relationship with the teen was reportedly discovered when a church deacon saw on Schaap's cellphone a picture of Schaap and the teenager kissing.
The ex-pastor -- long known for his fiery sermons -- previously pleaded guilty to the federal charge of taking a minor across state lines with intent to engage in criminal sexual activity.
Schaap and his wife Cindy, the daughter of a beloved former pastor, have been married for more than 30 years and have two children. Schaap had made a career writing advice books about dating in addition to overseeing the megachurch, one of the nation's largest.