We shall learn from Romans 10:9 that believing in the heart that Christ resurrected cannot be made by the natural man. This is because his heart is dead, stony and corrupted by the Adamic sin. He cannot produce works of righteousness pleasing or acceptable to God.
For the natural man to be saved, he must be one of those chosen by the father before the world began and given to Christ to die for. Such, the Holy Spirit will apply the Word to their hearts as they come under the Gospel hearing. At each person's appointed time, he will be given a new life and become born into the kingdom of God. They will believe Christ from their hearts and begin to live to God's glory and with eternity in view.
Amen