Augustine of Hippo
"Our belly has cleaved to the earth" (Ps 43:25), that is, our belly was in agreement with the impiety of this dust. For this is what is meant by "cleaved."
"But for me it is good to be near God." You are near to God when you agree with God. It is not without reason that our belly is said to have cleaved to the earth.
This indicates those who, not having endured persecution, agreed with the enemies. This is why they cleaved to the earth.
But why are they called the belly, if not because they are carnal? As the mouth of the Church is found in the saints and the spiritual, so the belly of the Church is found in the carnal.
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Thus the mouth of the Church is manifest, while the belly is hidden as more delicate and weaker. Scripture indicates this in a certain place, where someone says that he received a book.
This book, he says, was sweet in his mouth and bitter in his belly. In Rev 10:9 and in Ps 43:25, the Vulgate uses the same word, venter.
What is this, if not the higher commandments, which the spiritual receive and the bodily do not receive? The spiritual rejoice in them, and the bodily are grieved by them.
What does this book contain, brethren? "Sell all that you have and give to the poor" (Mt 19:21). How sweet this sounds in the mouth of the Church. All the spiritual have done so.
But if you say to some carnal man, "Do this," he will sooner go away from you sorrowful, like that rich man from the Lord (cf. Mk 10:21-22), than do what is said.
Why did he go away sorrowful, if not because that book is sweet in the mouth and bitter in the belly?