Reformed theologian John Piper recently tackled a controversial issue within the church: sexual impurity vs. homosexuality.

On an "Ask Pastor John" broadcast this week, the "Desiring God" author was asked whether he would marry a couple who were already living together and if so, how that would be different from marrying a homosexual couple.

In response, Piper said he would marry a heterosexual couple who were cohabiting only if they genuinely repented of their sin and remained chaste until marriage.

"That bears a beautiful testimony of the grace of God in their lives," the pastor said, noting that failing to remain abstinent prior to marriage is not an unforgivable sin.

"Purity on the other side of sin is possible through the justifying and sanctifying work of Christ," he noted.

However, Piper says that while there is also forgiveness for a cohabitating homosexual couple if they repent of their sin of sexual relations outside of marriage, he would not participate in marrying such a couple.

He clarifies: the heterosexual couple is "moving out of sin of fornication ... marrying in accordance of God's ordinance and they're not sinning in the marriage, whereas the same-sex couple are moving out of a sinful relationship (of cohabiting) and are about to move into another one (marriage)."

Homosexual behavior within itself is a sin, Piper notes, referencing 1 Corinthians 6:9-10 which states, "Or do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor men who have sex with men nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God."

"There is no such thing as homosexual marriage, it doesn't exist, it's a mirage in our culture. The Bible knows nothing of it and therefore it can't be used as a warrant in order to justify homosexual behavior," the Piper stated.

However, the renowned theologian ended his discussion by reinforcing that no matter what kinds of sexual sin people engage in, God is ready and waiting to forgive those who turn to him in repentance and faith.

"God holds out hope for all sinners who will turn away from the sins of the past ... and move forward into lives of holiness," he concluded.