How do we approach God after the cross?
After the cross, sinners approach God on the basis of Christ's blood, not animal blood. Before Christ died, animal blood was the basis; on this side of the cross, Christ's shed blood is the basis. The four gospels record the time before His crucifixion, so they belong to the Old Testament.
Les explains that once Jesus ascended back to glory, there is no direct communication between Him and sinful men except through the apostle Paul. Paul claims over and over that he saw the Lord face to face and that the Lord revealed these things to him. The key difference is the basis of approach: before Christ died, sinners approached God on the basis of animal blood; on this side of the cross, we approach God on the basis of Christ's blood. Because everything in the gospels is before Christ is crucified, there is nothing in the four gospels about the shed blood of Christ—it hadn't happened yet. Paul, however, knows Christ crucified, as he writes in Galatians 1:11 and as will be seen in 1 Corinthians 1:18. Les notes the opposition he encounters from people who want nothing to do with Paul's letters, but he emphasizes that Paul's revelation from the ascended Christ makes all the difference.