When does God give a believer a new divine nature?
God imparts a new divine nature when the old Adam dies, which happens when a person is in Christ and becomes a new creation. This new nature is placed there by an act of God, is divine, and cannot sin, though the old flesh remains and can still trip us up.
Les explains that because of His work of the cross, if any man be in Christ, he is a new creation; old things are passed away, and all things become new. In other words, when old Adam dies, God again imparts to us a new divine nature. That new nature is divine, placed there by an act of God, and cannot sin. However, we still have the old flesh, the old Adam, which is still capable of tripping us up, but so far as the new man is concerned, it cannot sin.