After sharing a parable about a wedding feast in Matthew 22, Jesus concluded with this statement: "Many are called, but few are chosen" (v. 14). Of all those who are summoned or invited to the marriage supper of the Lamb (see Revelation 19:9)--to salvation--only a few believe. He said that few are chosen because those who believe discover that they have, in fact, been chosen--they are the elect.
I won't bog you down with all the fine points, but there are two perspectives in Scripture, given hand in hand and perfectly aligned with each other: the election of God and the freedom of choice a human being possesses to cooperate with the summons. When a person decides to follow Christ, they discover that while they thought they chose Jesus, Jesus actually chose them. As Jesus said to His disciples, "You did not choose Me, but I chose you" (John 15:16). On one hand you have human volition making the choice to follow, but on the other hand you discover, "Oh, I've been part of the elect all along."
The theological term for this is prevenient grace. Prevenient grace is the concept that the one who seeks the Lord discovers that they have been sought by the Lord in the first place. But in the process of being elect, they also, by their own free will, make the choice to follow Him.
These two things don't contradict each other; they are perfectly aligned. One is from the divine perspective and one is from the human perspective. You and I don't understand God's perspective--He's omniscient. He knows everything that has happened or will happen from eternity past to eternity future, thus He can say, "You didn't choose Me; I chose you all along." As Jesus said, "No one can come to Me unless the Father who sent Me draws him" (John 6:44). But it's the coming together of this prearrangement and human choice: you have been elected by God, yet you are summoned and invited to come, and it takes the cooperation of your free will.
Both sides are true, and there is no conflict. It is a seeming contradiction but really no contradiction at all. It's like light: light is an apparent contradiction because it behaves both like a wave and like a particle, even though science will tell you that there can only be one or the other. Light has both properties; it's an apparent contradiction, but that's the way it is. So it is with my free will to choose and God's sovereign calling and election of choosing me.
"Many are called, but few are chosen." Let that inspire in you a heart of thankfulness and gratitude--that the Lord chose you and called you and that you responded to His call.