53 I am not ignorant how much the grandeur of the divine mystery baffles our weak understanding, so that language can scarcely express it, or reason define it, or thought even embrace it. The Apostle, knowing that the most difficult task for an earthly nature is to apprehend, unaided, God's mode of action (for then our judgment were keener to discern than God is mighty to effect), writes to his true son according to the faith, who had received the Holy Scripture from his childhood, As I exhorted you to tarry at Ephesus, when I was going into Macedonia, that you might charge certain men not to teach a different doctrine, neither to give heed to fables and endless genealogies, the which minister questionings, rather than the edification of God which is in faith. He bids him forbear to handle wordy genealogies and fables, which minister endless questionings.
The edification of God, he says, is in faith: he limits human reverence to the faithful worship of the Almighty, and does not suffer our weakness to strain itself in the attempt to see what only dazzles the eye. If we look at the brightness of the sun, the sight is strained and weakened: and sometimes when we scrutinise with too curious gaze the source of the shining light, the eyes lose their natural power, and the sense of sight is even destroyed. Thus it happens that through trying to see too much we see nothing at all.
What must we then expect in the case of God, the Sun of Righteousness? Will not foolishness be their reward, who would be over wise? Will not dull and brainless stupor usurp the place of the burning light of intelligence? A lower nature cannot understand the principle of a higher: nor can Heaven's mode of thought be revealed to human conception, for whatever is within the range of a limited consciousness, is itself limited. The divine power exceeds therefore the capacity of the human mind.
If the limited strains itself to reach so far, it becomes even feebler than before. It loses what certainty it had: instead of seeing heavenly things it is only blinded by them. No mind can fully comprehend the divine: it punishes the obstinacy of the curious by depriving them of their power. Would we look at the sun we must remove as much of his brilliancy as we need, in order to see him: if not, by expecting too much, we fall short of the possible. In the same way we can only hope to understand the purposes of Heaven, so far as is permitted.
We must expect only what He grants to our apprehension: if we attempt to go beyond the limit of His indulgence, it is withdrawn altogether. There is that in God which we can perceive: it is visible to all if we are content with the possible. Just as with the sun we can see something, if we are content to see what can be seen, but if we strain beyond the possible we lose all: so is it with the nature of God. There is that which we can understand if we are content with understanding what we can: but aim beyond your powers and you will lose even the power of attaining what was within your reach.
Source: On the Trinity (New Advent)