What is the spiritual parallel to having children in a physical marriage?
Just as God expects a physical marriage to produce children, He expects believers to produce other believers. This fruit is soul winning, which must be done scripturally. The fullness of the Gentiles arrives when the Body of Christ is complete, pictured as a baby fully formed in the womb before delivery.
Les teaches that in a physical marriage God expects the fruit of that marriage to be children, and so also the fruit of believers should be other believers. He calls this soul winning, and it has to be done scripturally. He connects this to Romans 11:25, where Israel's partial blindness lasts until the fullness of the Gentiles is brought in. Les identifies the fullness of the Gentiles as the time when the Body of Christ is complete. He uses the analogy of a baby in the womb: when the mother's womb has finished forming every part of that little body to the last cell, then delivery comes. Likewise, when God has finished drawing in the last person coming into the Body of Christ, believers are out of here, and then He can pick up and finish.