Why the Church refers to the Fathers and Doctors, including St Augustine especially, is clear.
churchinhistory.org/pages/booklets/augustine.htm
'Now, while Augustine’s defence of marriage is centred on its procreative finality, it is inexact to suggest that he had (to use the modern expression) no “personalist” understanding of the conjugal relationship. In his treatise on Continence, he strongly defends the goodness of sexual difference and of the union of husband and wife. [6] Of particular importance is his work
De bono coniugali, written to refute the accusation of Manicheism made by Jovinianus against the Catholics.
'In the opening chapter, Augustine clearly sets forth the broad human foundation on which he grounds the goodness of marriage: man’s sociable nature and the natural value that man finds in friendship. It is only after laying down that human sociability finds its first natural expression precisely in marital society, that he goes on to indicate what it is that distinguishes the married relationship: i.e., the fact that it involves a man and a woman not in any mere ordinary friendship, but in a procreative society. [7]
'Elsewhere in the same work, within the dominant concept that marriage is meant for procreation, we find further clear notes of what may be termed conjugal personalism. Augustine argues explicitly that there are other ends to marriage, besides procreation, which also make it good. Observing that “it is proper to inquire for what reason marriage be good,” he goes on, “And this seems to me not merely to be on account of the begetting of children, but also on account of the natural association between the two sexes,” [8] whose mutual faith he describes as “the first fellowship of humankind in this mortal state.” [9]
’He insists on the value of love between husband and wife, and how the ordo caritatis unites those whom age or misfortune may have deprived of children: "Now in good although aged marriage, even if the vigour of youth between man and woman has faded, the order of charity between husband and wife remains in its fullness." [10]
'He presents fidelity as an exchange of mutual respect and service, [11] and insists too that “the bodies of the married too are holy, when they keep faith to one another and to God.” [12] And in his later work on widowhood, he writes: "The good of marriage is always a good indeed. In the people of God it was at one time an act of obedience to the law; now it is a remedy for weakness, and for some solace of human nature.”[13]
The “bona” of matrimony
’As can be seen from these passages, Augustine is conscious not only of the procreative ordering of marriage, but also of its unitive value….Augustine’s doctrine of the triple bona of marriage—proles, fides, sacramentum [14] — should be read not merely in an institutional context (as is normally done), but also precisely in personalist terms. The penetrating analysis of the three-fold matrimonial bona has never lost relevance over 1500 years.’ [15]