The Great Commandment and Summary of the Law say: Love God with all your heart, mind, soul, and strength, and your neighbor as yourself — and your neighbor is whoever happens to cross your path.
Jesus said that if we observe these, we will gain eternal life.
But these commandments come straight from the Hebrew Scriptures, aka the Old Testament.
Craig, a correspondent on the TitusOneNine blog, asked: What, then, is the difference between a Christian and a Jew?
Under Jesus’ definition, there’s no material difference between a good Christian and a good Jew. (That makes sense; after all, Jesus and his original followers were Jews.)
It was only after Jesus' death that his later followers and his Jewish compatriots excluded each other from fellowship.
If Jesus had still been around, I don’t think he would have put up with that.
 Luke 10.25-37 tells how Jesus explained the Great Commandment and Summary of the Law:
On one occasion an expert in the law stood up to test Jesus. “Teacher,” he asked, “what must I do to inherit eternal life?”
“What is written in the Law?” he replied. “How do you read it?”
He answered: “ ‘Love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind’; and, ‘Love your neighbor as yourself.’”
“You have answered correctly,” Jesus replied. “Do this and you will live.”
But he wanted to justify himself, so he asked Jesus, “And who is my neighbor?”
In reply Jesus [tells the parable of the Good Samaritan]. * * *
“Which of these three do you think was a neighbor to the man who fell into the hands of robbers?”
The expert in the law replied, “The one who had mercy on him.” [Editorial comment: I wonder if a better translation might be “The one who practiced acts of mercy toward him.”]
Jesus told him, “Go and do likewise.”