1 Cor 1:18, 23-24, Lk 10:21, Rom 10:9
God saved believers through evangelism. Evangelism is preaching that Jesus is the Christ. (1 Cor 1:21)
1 Cor 1:21 For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe.
Evangelism is preaching that Jesus accomplished all the work of Christ on the cross. (1 Cor 1:18,23-24, Rom 10:9)
1 Cor 1:18 For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God. 23 But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness; 24 But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God. Rom 10:9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
God has hidden the secret of evangelism from the wise. (Lk 10:21)
Lk 10:21 In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father; for so it seemed good in thy sight.