It is ingrained in all living creatures, first of all, to preserve their own safety, to guard against what is harmful, to strive for what is advantageous.
AmbroseWe ask for what reason our Lord was unwilling to state the time of His coming (cf. Mk. 13:31-32). If we ask it, we shall not find it is owing to ignorance, but to wisdom. For it was not to our advantage to know; in order that we being ignorant of the actual moments of judgment to come, might ever be as it were on guard, and set on the watch-tower of virtue, and so avoid the habits of sin; lest the day of the Lord should come upon us in the midst of our wickedness.
AmbroseThe Lord Jesus himself proclaims, 'This is My Body.' Before the blessing of the heavenly words something of another character is spoken of; after consecration it is designated 'body'. He himself speaks of his blood. Before the consecration it is spoken of as something else; after the consecration it is spoken of as 'blood'. And you say, 'Amen', that is, 'It is true.' What the mouth speaks, let the mind within confess; what the tongue utters, let the heart feel.
AmbroseIf you have two shirts in your closet, one belongs to you and the other to the man with no shirt.
Ambrose... these three witnesses are one, as John said: 'The water, the blood, and the Spirit' (I Jn. 5:8). One in the mystery, not in nature. The water, then, is a witness of burial, the blood is a witness of death, the Spirit is a witness of life. If, then, there be any grace in the water, it is not from the nature of water, but from the presence of the Holy Spirit.
Ambrose