"I am asking if the gospel that Paul preached is essentially the same or different from the message of Jesus. A very good case can be made, of course, that they are fundamentally different."
I have asserted however that this is not the case and Rabbi Cohen presented to me Matthew 5:19 -20, 19:17 with Gal 2:21 to demonstrate how Jesus and Paul teach contradictory messages and I hope to respond to them to the best of my ability in this article.
Let's look at the texts.
Firstly Matthew 19:17 and also Mark 10:18 connects with this too:
"16 Just then a man came up to Jesus and asked, “Teacher, what good thing must I do to get eternal life?”
28 Jesus said to them, “Truly I tell you, at the renewal of all things, when the Son of Man sits on his glorious throne, you who have followed me will also sit on twelve thrones, judging the twelve tribes of Israel. 29 And everyone who has left houses or brothers or sisters or father or mother or wife[e] or children or fields for my sake will receive a hundred times as much and will inherit eternal life. 30 But many who are first will be last, and many who are last will be first."
17 “Why do you ask me about what is good?” Jesus replied. “There is only One who is good. If you want to enter life, keep the commandments.”
18 “Which ones?” he inquired.
Jesus replied, “‘You shall not murder, you shall not commit adultery, you shall not steal, you shall not give false testimony, 19 honor your father and mother,’[c] and ‘love your neighbor as yourself.’[d]”
20 “All these I have kept,” the young man said. “What do I still lack?”
21 Jesus answered, “If you want to be perfect, go, sell your possessions and give to the poor, and you will have treasure in heaven. Then come, follow me.”
22 When the young man heard this, he went away sad, because he had great wealth.
23 Then Jesus said to his disciples, “Truly I tell you, it is hard for someone who is rich to enter the kingdom of heaven. 24 Again I tell you, it is easier for a camel to go through the eye of a needle than for someone who is rich to enter the kingdom of God.”
25 When the disciples heard this, they were greatly astonished and asked, “Who then can be saved?”
26 Jesus looked at them and said, “With man this is impossible, but with God all things are possible.”
27 Peter answered him, “We have left everything to follow you! What then will there be for us?”
In the context, Jesus is not teaching you are saved by keeping the commandments, what he is doing is testing the man who is enquiring of him. He knows that the man is an idolater for loving his riches. The man claims to have kept all the commands, to which Jesus refutes because of his request to "sell all your possessions then come follow me". The man was exposed as an idolater because he loved his riches more than God. Jesus in the context demands that a person should be willing to forsake all to follow him, which would be blasphemy for a mere man to say and only God should be given that devotion.
Jesus also emphasises that only God is capable of saving a man as man cannot save himself by the works of the law. Yes Jesus does call for obedience to God (Which Paul also does I may add) but it is not your works that merit your salvation.
Now onto Matthew 5:19:
"Matthew 5:17 “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18 For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. 19 Therefore anyone who sets aside one of the least of these commands and teaches others accordingly will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven. 20 For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven."
Jesus is referring to his goal that he is coming to accomplish and that he is not setting aside the Law and the Prophets. This doesn't mean that Gentiles are to observe the Torah in it's entirety and I write on this subject here: http://answering-judaism.blogspot.co.uk/2013/11/observance-of-torah-demanded-of-gentiles.html
Fulfilling of the law is not the same as abolishing it. Jesus fulfills the demands that the Torah requires and thus there are certain commands that needn't be carried out by virtue of him fulfilling those requirements. I also direct people to this article for other pieces of information regarding the laws pertaining to women raised by Yehuda Yisroel and others: http://answering-judaism.blogspot.co.uk/2014/01/the-good-bad-or-strange-fulfillment.html
Finally we read in Galatians 2:21:
"15 “We who are Jews by birth and not sinful Gentiles 16 know that a person is not justified by the works of the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in[d] Christ and not by the works of the law, because by the works of the law no one will be justified.
19 “For through the law I died to the law so that I might live for God. 20 I have been crucified with Christ and I no longer live, but Christ lives in me. The life I now live in the body, I live by faith in the Son of God, who loved me and gave himself for me. 21 I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing!”[e]"
17 “But if, in seeking to be justified in Christ, we Jews find ourselves also among the sinners, doesn’t that mean that Christ promotes sin? Absolutely not! 18 If I rebuild what I destroyed, then I really would be a lawbreaker.
The law itself didn't bring righteousness to men and was there to show how bad man really is. Keep also in mind that the Torah wasn't kept to get out of Egypt in the TANAKH, but what does transpire is the people kept the Torah out of gratitude to God for getting them out of Egypt, not to keep it to get out of Egypt.
The law is pure and good and holy, but man cannot be justified by observance of it and it is by God's grace that they can be saved. The obedience was prepared in advance for the righteous whom YHWH has drawn.
The texts in context do not prove the assertion of Rabbi Cohen or others reading the texts.
Hope this article helps.
For other articles on Paul, read the following: