What was Christ’s purpose in speaking the words He did on the last day of the Feast of Tabernacles regarding the descent of the Holy Spirit?

It was the custom of the Jews to leave their homes during the Feast of Tabernacles and live in temporary tents for a week to remind them that they were strangers and lodgers in this world. During the first seven days of the feast, they would bring water from the Pool of Siloam in a golden vessel, and the High Priest would pour it out in front of the people, announcing that whoever was thirsty should approach and drink. This was a type of the rock from which water flowed for the people in the wilderness (Ex. 17:6). But on the eighth day, they would not bring water from the pool, indicating that the people will now drink from the springs of Canaan, and not from the water of the wilderness. It was on this day that the Lord Christ, the great High Priest, stood and offered Himself as the spring of water that overflows with Living Water in the depths of the souls of the faithful; inviting them to drink joyfully from the wells of salvation (Isa. 12:3; Zech. 14:8).

The Gospel of John tells us, “On the last day, that great day of the feast, Jesus stood and cried out, saying, ‘If anyone thirsts, let him come to Me and drink. He who believes in Me, as the Scripture has said, out of his heart will flow rivers of Living Water.’ But this He spoke concerning the Spirit, whom those believing in Him would receive; for the Holy Spirit was not yet given, because Jesus was not yet glorified” (John 7:37–39).

793 St. Irenaeus of Lyon, Against Heresies 5.36.2 (ANF 1:567; PG 7:1223B).

794 St. Irenaeus of Lyon, Against Heresies 4.38.3 (ANF 1:521; PG 7:1108B).

From this divine promise of the descent of the Holy Spirit we can learn the following:

First: those who followed the prophet Moses drank water from the rock in the wilderness where that rock followed them and overflowed with thirst-quenching water. This rock is a type of the Lord Christ (1 Cor. 10:4). Whosoever believes in Christ carries the Rock within himself, and from his inner person he overflows with that which builds up the Kingdom of God.

Second: the Jews called running water “living water,” because it is constantly in motion. If the Lord Christ indeed dwells within the heart of a believer, the Holy Spirit continually works in him, giving him grace upon grace, which graces overflow upon those around him (Prov. 10:11). But it is not enough for us to drink from the streams that flow within us, content merely to rest in divine grace; we must also let these inner streams overflow and water many. Then, the parched land will not only become itself a garden, but its waters will also overflow upon many parched souls and transfer the nature of a paradise to them, fresh and fruitful.

Third: on the last day of the feast, the Lord Christ issued an invitation to the people returning to their homes. The last day was dedicated to Israel alone. That is why the eighth day was considered an especially worthy High Day.

Fourth: St. Ambrose draws a connection between this living spring to which the Lord Christ refers and the words we find in the book of Revelation when he says, “And this, again, is not a trivial matter that we read that a river goes forth from the throne of God. For you read the words of the Evangelist John to this purport: ‘And He showed me a river of living water, bright as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street thereof, and on either side, was the tree of life, bearing twelve kinds of fruits, yielding its fruit every month, and the leaves of the tree were for the healing of all nations’ (Rev. 22:1–2). This is certainly the River proceeding from the throne of God, that is, the Holy Spirit, Whom he drinks who believes in Christ, as He Himself says (John 7:37–38).”⁷⁹⁵