Around 100 years ago, liberals were driving a big wedge between Paul and Jesus; something similar is still happening today. For example, some people say that Jesus was a nice teacher of morals (the first Christian and a martyr for the cause), but Paul came in and messed it all up with detailed doctrine. Machen responded to this liberal teaching quite well in The Origin of Paul’s Religion (in 1925). In chapter 4, for example, Machen does a nice job showing how Paul, as an apostle commissioned by Jesus, agreed with Jesus in his teaching and preaching. Here are two paragraphs I really appreciated:
The details of Jesus’ earthly ministry no doubt had an important place in the thinking of Paul. But they were important, not as an end in themselves, but as a means to an end. They revealed the character of Jesus; they
showed why He was worthy to be trusted. But they did not show what He had done for Paul. The story of Jesus revealed what Jesus had done for others: He had healed the sick; He had given sight to the blind; He had
raised the dead. But for Paul He had done something far greater than all these things—for Paul He had died.
The religion of Paul, in other words, is a religion of redemption. Jesus, according to Paul, came to earth not to say something, but to do something; He was primarily not a teacher, but a Redeemer. He came, not to teach men how to live, but to give them a new life through His atoning death. He was, indeed, also a teacher, and Paul attended to His teaching. But His teaching was all in vain unless it led to the final acceptance of His redemptive work. Not the details of Jesus’ life, therefore, but the redemptive acts of death and resurrection are at the center of the religion of Paul. The teaching and example of Jesus, according to Paul, are valuable only as a means to an end, valuable in order that through a revelation of Jesus’ character saving faith may be induced, and valuable thereafter in order that the saving work may be brought to its fruition in holy living. But all that Jesus said and did was for the purpose of the Cross. “He loved me,” says Paul, “and gave Himself for me.” There is the heart and core of the religion of Paul.
J. G. Machen, The Origin of Paul’s Religion, p.167 (ch. 4)