Jesus said that Christianity was not to be preached to the Gentiles

Jesus wanted Christianity to be preached exclusively to the Jews, not to other nations. We have clear evidence of this in the Bible.

The Gospel According to Matthew – Chapter 10
5 These twelve Jesus sent out and commanded them, saying, "Do not go into the way of the Gentiles, and do not enter any city of the Samaritans;"
            These are very harsh words against the evangelization of non-Jewish and non-Semitic nations. Samaritans were practically a semi-Jewish denomination; the inhabitants of Samaria were partly of Jewish faith. So, Jesus forbade even semi-Jews from preaching the gospel to them, let alone Jews.
In the explanatory notes in the Catholic Bible, we find the following:
Samaria, the central province of Palestine, is named after its original capital, Samaria. It was inhabited by Samaritans, a people of various tribes and nations settled there after 720 BC by the Assyrian king Sargon II and his successors. The Samaritans partially adopted the Jewish religion but also retained many pagan superstitions and customs. Around 400 BC, they built their own sanctuary on Mount Gerizim (near Shechem – today's Nablus). Due to their mixed, "impure" origin and semi-pagan religion, they were a thorn in the side of the Jews.