Paul’s argument in this passage is this: if Christ laid down His life for sinners, how much more will he preserve the lives of those who are His children?
God called us while we were sinners. Christ did not come to save the ‘righteous’ but those who know themselves to be sinful men and women. This salvation was accomplished by the sacrifice of God’s only Son; the greatest sacrifice that could be made. How much more will God preserve, by the work of His Spirit, those for whom He has given this sacrifice?
If we can see the work of the Spirit in our lives, then we have a secure hope that God will preserve our lives to the end. This should cause us to rejoice greatly in God throught Christ.