The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned.
—1 Corinthians 2:14
The Holy Spirit is God's abiding gift, God's seal and promise. The Spirit is our assurance that what he began with Jesus' sacrificial death and our participation in it through faith and baptism, he will bring to completion at Jesus' return. But the world cannot understand this great promise, just like it cannot understand much of Scripture. Without the gift of the Holy Spirit, their eyes only see what they can touch with their fingers and cannot fully see what is true in God's heart and revealed in his Word.