“The Spirit explores the depths of everything, even the depths of God” (1 Cor 2:10)
While the gift of knowledge helps us to withdraw from the attraction of creatures, recognising in an inner sight their nothingness (inasmuch as they were created out of nothing), and makes us realise that all life and beauty proceed from God; the gift of understanding helps us to penetrate the mystery of God with the light of the Holy Spirit Himself.
Our understanding is not capable of penetrating the divine mysteries with the help of faith alone, even if we hold fast to the revealed truths. For faith is, on the one hand, a great light, but, on the other hand, it is still dark. It is a light in that it conveys to us the truth about God and about all that we need for the path of following Christ. But it does not allow us to penetrate into the mystery of God himself, nor to understand his Being from within. The knowledge of God remains somehow obscure. St. Paul directs our gaze to eternity, where we will see God face to face: