This is the description of the apostles. The Bible backs it up with accounts of them following Jesus, going out and preaching both before and after the crucifixion and resurrection, and healing and casting out demons. After Judas betrays Christ and hangs himself, the eleven get together and vote to choose one to take his place. They are very careful to choose from the ones who have been with them the whole time they were with the Lord. They pray and then vote. Matthias is chosen. This is in Acts 1:21-26.
Another event soon presents itself. Christ has chosen someone to go to the Gentiles. He meets Saul on the road to Damascus. Saul becomes Paul the apostle, one whom Christ sent. First Corinthians 9:1 bears this out. And these are the known apostles according to the Bible. The canonization of the Bible, which includes the New Testament, was completed by the fourth century (397 A.D.). Since it is complete, it is finished and all that is needed. All that God planned has been done. Everything needed for salvation of mankind is now available.
The sermon was one of clarification. There are those who think that there are still apostles in the world today. In order to be an apostle, one has to have been ordained by Jesus himself. And, he would have been given powers to heal and cast out demons. The apostles were the ones that brought the legacy of Jesus Christ to the world through preaching and writings made possible through the inspiration of God. God warns us not to add to his words. It’s in Proverbs 30:5-6.