The reason the apostle uses this terminology, "the foolishness of preaching," is not because there is any foolishness in the gospel, but because unbelievers view it as foolishness. Gospel preaching only saves believers, and even then it does not save them in an eternal sense. Eternal salvation is by grace, not by the gospel. 

    In order for unbelievers to be saved eternally by a message,----if such a thing were possible----that message would have to be one that appealed to them; one that pleased the ears of unregenerate men and women. But the message contained in the gospel of Jesus Christ is foolishness to those who are in a perishing state (See I cor. 1:18), and a stumblingblock to the unbelieving Jews (ver. 23). Therefore the gospel of Christ cannot be the means of saving anyone who looks upon it as foolishness. It cannot even save them in a timely sense, for they will not embrace it. None of us believe or benefit from, a message that we consider foolish or nonsensical. 

    The true gospel brings tidings that are good only to those who have been made "meek" by the inward work of the Holy Spirit. To those whose hearts have been broken and softened by a felt sense of their own wretchedness, unworthiness, and spiritual poverty, the gospel has the effect of "binding up" or healing. It proclaims liberty to those who have been held captive to the bondage of religious ignorance and error. It deals with the spotless life of Christ and His propitiatory sacrifice for the sins of His people, and it comforts those who mourn (See Isaiah 61:1-2). It is a preparation suitable only to those who have been graciously fitted to receive it. "The poor (the poor in spirit) have the gospel preached to them" (Matt. 11:5 & Luke 7:22). Unto those who are saved (already eternally saved) the gospel is the power of God (I Cor. 1:18), and unto them which are called (already called of God) it is "the power of God, and the wisdom of God" (ver. 24). The others reject it, because to them it is nothing but foolishness. 

    The true gospel does not bring life and immortality; it only brings these "to light" (II Tim. 1:10), and it instructs "the man of God" in righteousness and thoroughly furnishes "him" unto all good works (II Tim. 3:16). There is "another gospel" that the unsaved will receive but they will have no part of the gospel of Christ.