St. Hilary now expands upon the metaphor of the tree near the stream of waters:
In the book of Genesis (2:9), where the lawgiver depicts the paradise planted by God, we are shewn that every tree is fair to look upon and good for food; it is also stated that there stands in the midst of the garden a tree of Life and a tree of the knowledge of good and evil; next that the garden is watered by a stream that afterwards divides into four heads. The Prophet Solomon teaches us what this tree of Life is in his exhortation concerning Wisdom: She is a tree of life to all them that lay hold upon her, and lean upon her (Proverbs 3:18). This tree then is living; and not only living, but, furthermore, guided by reason; guided by reason, that is, in so far as to yield fruit, and that not casually nor unseasonably, but in its own season. And this tree is planted beside the rills of water in the domain of the Kingdom of God, that is, of course, in Paradise, and in the place where the stream as it issues forth is divided into four heads. For he does not say, Behind the rills of water, but, Beside the rills of water, at the place where first the heads receive each their flow of waters. This tree is planted in that place whither the Lord, Who is Wisdom, leads the thief who confessed Him to be the Lord, saying: Verily I say unto thee, to-day shalt thou be with Me in Paradise (Luke 23:43).
St. Hilary begins by reminding us that one of the trees within the Garden of Eden is the Tree of Life. He then reminds us that Solomon (author of Proverbs) equates Wisdom with the Tree of Life and that everyone who holds onto her (Wisdom) is happy. The river that divides in four evokes the Four Evangelists and the Gospel that they proclaim, whereat the Tree that is the Cross is planted. This Tree, of course, is now the Tree of Life whose fruit — our Lord, God and Savior Jesus Christ — offers paradise and eternal life to all who partake — as does the thief who believes that Christ is the Only-Begotten Son given by the Father so that all who believe might have eternal life (John 3:16).
In other words, part of the happiness the blessed man has and holds onto is the hope offered by the Cross — the Kingdom of Heaven.