P.T. Forsyth writes of the work of Christ on the cross:
The sacrifice of the Cross was not man in Christ pleasing God; it was God in Christ reconciling man, and in a certain sense, reconciling Himself. My point at this moment is that the Cross of Christ was Christ reconciling man. It was not heroic man dying for a beloved and honoured God; it was God in some form dying for man.
– P.T. Forsyth, The Work of Christ (Wipf and Stock, 1996).
The work of Christ on the cross was that work which made possible the full and complete forgiveness of God and our reconcilation to him. We need forgiveness for our rebellion or resistance against God through our sin and we need reconciliation to God because our sin separates us from God. I know Sam said God doesn’t need the cross to forgive, but I think he’d agree (maybe, maybe not) the cross is the most complete picture of God’s forgiving love – that, he himself, in and through the person of Jesus of Nazareth, completed the work of redemption by forgiving our sin and reconciling us to him. He knew we could not reconcile ourselves to him – so, in grace (favor) and in faithfulness to his covenant promises, he did it for us in and through the cross, which was then completed in and through the resurrection of Jesus from the dead.
ps. I recognize my theology of the cross still needs work and is always in process.