When will an unbeliever understand the gospel?
An unbeliever understands the gospel only when God opens their eyes and hearts, because the natural, unsaved man cannot receive or know the things of the Spirit; they are spiritually discerned. This occurs at God's own good timing, so believers should remain patient with unbelievers until He grants that understanding.
Les teaches from 1 Corinthians 2:13-14 that spiritual things are taught by the Holy Spirit, comparing spiritual things with spiritual. The natural man, the unconverted, unregenerated, unsaved, lost man, receiveth not the things of the Spirit of God, for they are foolishness unto him. He cannot understand or know them because they are spiritually discerned. Therefore, as Les explains, we must be real patient with unbelievers, even if it takes three years for them to come to the place of understanding the gospel. He hopes it would be quicker, but he remains patient because he realizes they cannot comprehend these things until God opens their eyes and hearts, and we leave that to His own good timing. Earlier he noted that when a person becomes a believer, they will comprehend the Scriptures.