Was the salvation of the whole human race revealed at the death and resurrection of Christ?
No. At the death, burial, and resurrection of Christ, God had not yet revealed that the salvation of the whole human race was wrapped up in those events. He was still dealing with Israel on the grounds of covenant promises. That secret would come a little later.
Les explains that the secret of all God's purposes in Christ's going to the cross was not yet revealed at that time. God is sovereign and has the prerogative of keeping things secret until He reveals them, as Deuteronomy 29 states; when He reveals it, He expects mankind to believe it. This is the whole scope of Scripture. He had not yet revealed that in the death, burial, and resurrection was wrapped up the salvation of the whole human race, but was still dealing with Israel on the grounds of those covenant promises. That revelation would come later, connected to the outcalling of the Church through Saul of Tarsus.