This was in last month's Magnificat (p. 347) and I thought it worth reproducing since it speaks to the fallacy of gnosticism and the need to look to nature to understand God.
A thing is not true just because I need it, for need does not create truth, but only directs us to it. Or am I forbidden to ask whether the miracle of the Incarnation is true? Must I even believe it just because it is not true for my critical thought? And is faith therefore essentially a conflict and contradiction? That could only be if God were not merely something different from me, but something essentially opposite; if my whole being were sin. Then I should in truth possess in myself no means of access to God. I should be darkness unpenetrated by God's light; I should be a corpse, and his life flowing round me. But am I a corpse? Am I only sin? No, I am not. I have sin, but I am not sin. I have death in me, but I am not dead. I have contrariety in me, but not pure negation, not absolute contradiction. Just for that reason my thought, for all its stumbling, can discern the problem of my being; and my will, however much it may waver, can desire the removal of my contrarieties in the God-Man. So faith in the Incarnation is not a miraculous flower growing in me without root; it has its root in my natural capacity for God, in what the theologians call a potentia obedientialis, and it is evoked therein by God. Therefore faith does not come to me without my co-operation. I must hold my soul ready for the living God, and I must hearken to him when he gives testimony of himself.
—Father Karl Adam, Christ Our Brother, trans. Dom Justin McCann (Collier Books, 1959).