Jesus told the disciples to preach the Gospel to all nations.
Go therefore and make disciples of all nations, baptizing them in
the name of the Father and of the Son and of the Holy Spirit (Matthew
But you will receive power when the Holy Spirit has come upon you, and
you will be my witnesses in Jerusalem and in all Judea and Samaria,
and to the end of the earth.” (Acts 1:8, ESV)
Paul wasn't the first one nor the only one who preached the Gospel to the Gentiles. According to Acts, Peter was the first to preach the Gospel to the Gentiles. Peter received a vision from the Lord and received a command to preach to the Gentiles in the house of Cornelius the gentile. The Gentiles were filled with the Holy Spirit and were baptized.
While Peter was still saying these things, the Holy Spirit fell on all
who heard the word. And the believers from among the circumcised who
had come with Peter were amazed, because the gift of the Holy Spirit
was poured out even on the Gentiles. For they were hearing them
speaking in tongues and extolling God. Then Peter declared, “Can
anyone withhold water for baptizing these people, who have received
the Holy Spirit just as we have?” And he commanded them to be baptized
in the name of Jesus Christ. Then they asked him to remain for some
days. (Acts 10:44-47, ESV)
Peter reported this to the believers in Jerusalem and they all glorified God.
When they heard these things they fell silent. And they glorified God,
saying, “Then to the Gentiles also God has granted repentance that
leads to life.” (Acts 11:18, ESV)