For the word of the cross is folly to those who are perishing, but to us who are being saved it is the power of God. (1 Corinthians 1:18 ESV)
It is not just the cross that is folly but the church and the means of grace tied to the cross that are folly to those who are perishing. Why, you ask? It is folly when it does not contribute to the goals of the heart. Our culture offers friendship, pleasure, success, new toys, exotic trips, etc. as goals of the heart. The cross does not contribute toward these goals, so it is folly to embrace it. This is why the health and wealth gospel is such a farce. It would seek to offer Jesus as a means of reaching your culturally-driven goals of the heart. I can’t tell you how often I have seen some enthusiastically receive Christ and join the church only to fade away a short time later when they realized that Jesus and His church haven’t solved the problems they wanted solved and brought them closer to their real goals of the heart, such as a quick fix for a troubled child, or financial rescue, etc.
The only way the cross changes from folly to wisdom is when these false goals of the heart (aka idols) are stripped away and revealed as false. When God opens our eyes to see that a right relationship with Him is the true longing of the heart (of which all of our false goals are mere shadows), then the cross is wisdom. It becomes the doorway to paradise.
I bless the Lord who gives me counsel; in the night also my heart instructs me. I have set the Lord always before me; because he is at my right hand, I shall not be shaken. Therefore my heart is glad, and my whole being rejoices… You make known to me the path of life; in your presence there is fullness of joy; at your right hand are pleasures forevermore. (Psalms 16:7-9, 11 ESV)