5 Yet, Brethren, this exceeding trouble is not in this ship, save only in the absence of the Lord. What! can he who is in the Church, have his Lord absent from him? When has he his Lord absent from him? When he is overcome by any lust. For as we find it said in a certain place in a figure, “Let not the sun go down upon your wrath: neither give place to the devil:” and this is understood not of this visible sun which holds as it were the zenith of glory among the rest of the visible creation, and which can be seen equally by us and by the beasts; but of that Light which none but the pure hearts of the faithful see; as it is written, “That was the true Light, which lightens every man that comes into the world.” For this light of the visible sun “lightens” even the minutest and smallest animals.
Righteousness then and wisdom is that true light, which the mind ceases to see, when it is overcome by the disordering of anger as by a cloud; and then, as it were, the sun goes down upon a man's wrath. So also in this ship, when Christ is absent, every one is shaken by his own storms, and iniquities, and evil desires. For, for example, the law tells you, “You shall not bear false witness.” If you observe the truth of witness, you have light in the soul; but if overcome by the desire of filthy lucre, you have determined in your mind to speak false witness, you will at once begin through Christ's absence to be troubled by the tempest, you will be tossed to and fro by the waves of your covetousness, you will be endangered by the violent storm of your lusts, and as it were through Christ's absence be well near sunk.
Source: Sermons on Selected Lessons of the New Testament (New Advent)