The first section of the parable of the Royal wedding (Matthew 22:1-7) is about the Jewish people. The entire nation was invited to follow the Lord Jesus, but many refused the invitation. After this, as many were invited as the servants could find (verses 8-13). The meaning is that the Gentiles were also called by the message of the Gospel. The offer of grace is for everybody. Still this does not mean that everybody will be saved. God's condition is that we must be clothed with Christ. The man who was not wearing a wedding garment was not covered by Christ. He thought he could partake in the wedding banquet on his own terms and therefore he was cast out.
The phrase "few are chosen" does not mean that the king had selected only a few people; on the contrary, the king had invited as many people as possible. But many of the invited guests were unwilling to come or wanted to come only on their own terms.
Those who came to the wedding and were wearing wedding garments, those are called "chosen" in this passage. These are relatively few in number, compared to all those who have been called but refuse to come, but it is still a multitude no one can count.