Ante-Nicene Fathers, Vol IX:
Epistle to Gregory and Origen's Commentary on the Gospel of John.: Chapter XXXIII

33.  Christ the True Vine, and as Bread.

To what we have said must be added how the Son is the true vine.  Those will have no difficulty in apprehending this who understand, in a manner worthy of the prophetic grace, the saying: 4609   “Wine maketh glad the heart of man.”  For if the heart be the intellectual part, and what rejoices it is the Word most pleasant of all to drink which takes us off human things, makes us feel ourselves inspired, and intoxicates us with an intoxication which is not irrational but divine, that, I conceive, with which Joseph made his brethren merry, 4610 then it is very clear how He who brings wine thus to rejoice the heart of man is the true vine.  He is the true vine, because the grapes He bears are the truth, the disciples are His branches, and they, also, bring forth the truth as their fruit.  It is somewhat difficult to show the difference between the vine and bread, for He says, not only that He is the vine, but that He is the bread of life.  May it be that as bread nourishes and makes strong, and is said to strengthen the heart of man, but wine, on the contrary, pleases and rejoices and melts him, so ethical studies, bringing life to him who learns them and reduces them to practice, are the bread of life, but cannot properly be called the fruit of the vine, while secret and mystical speculations, rejoicing the heart and causing those to feel inspired who take them in, delighting in the Lord, and who desire not only to be nourished but to be made happy, are called the juice of the true vine, because they flow from it.

Footnotes

Ps. civ. 15.

Gen. xliii. 34.