The unbeliever or the natural man cannot understand spiritual things. Understanding comes by the illumination of the Holy Spirit indwelling the believer. To the unbeliever, the things of God are foolishness to him. I recall as an unbeliever I heard for the first time the word “holiness”. It has no meaning to me. I do not understand what it means. I recall also not having any moral compass in the sense the I have not heard the laws of God as summarised in the Ten Commandments.