Why was Christ before the cross not the object of our salvation that He is after the cross?
Christ before the cross was not the object of salvation because salvation is made possible by the work of the cross—His death, burial, and resurrection. Although it is the same man and same God, believers are now attached to Christ after the cross, ascended in glory, not to Christ merely in His earthly ministry.
Les explains that Paul is not talking about knowing Christ merely after the flesh, that is, in His earthly ministry. Many preach about Jesus and His miracles, signs, and wonders Sunday after Sunday, but Paul says we know no man after the flesh. Paul lived contemporary with Christ, yet now, from His death, burial, and resurrection, we do not look back and know Him in His earthly ministry as such. It is the same man and the same God, but the Christ before the cross was not the object of our salvation that He is after the cross, because the work of the cross makes possible our salvation experience. Now He is ascended in glory, and that is the Christ believers are attached to.