Joh 7:37 And on the last, and great day of the festivity, Jesus stood and cried, saying: If any man thirst, let him come to me and drink.
Joh 7:38 He that believeth in me, as the scripture saith: Out of his belly shall flow rivers of living water.
On the last day, the great day of the feast, that is, the eighth day, Jesus cried aloud to the people assembled at the temple. His words mean: If anyone thirst spiritually, let him come to Me by faith, and grace shall be abundantly poured into his soul. The words: Out of his belly, &c., are nowhere to be found in the Old Testament; but, as signifying the abundance of grace in the new dispensation, they convey the sense of many passages of the Old Testament. See Is 41:18, 44:3; Ezek 34:25; Joel 2:28.
Joh 7:39 Now this he said of the Spirit which they should receive who believed in him: for as yet the Spirit was not given, because Jesus was not yet glorified.
The Evangelist gives an authentic interpretation of our Lord s words: For as yet the Spirit was not given. These words explain why our Lord spoke of the abundant outpouring of the Spirit as still to come, for the Holy Ghost was not yet given, inasmuch as Christ was not yet glorified (Jn 16:7). When it is said that the Holy Ghost was not yet given, the meaning is, that He was not yet given so abundantly, so manifestly, or so universally, as He has been since the first Pentecost. It is not meant that the Holy Ghost had not been given to the just of the Old Testament. They, as well as we, had the grace of the Holy Ghost in their souls; moreover, according to the common teaching of the fathers and theologians, they, like the just now, had the Holy Ghost united to their souls, not merely by His grace, but also by a substantial union. This union is not, however, peculiar to the Holy Ghost, but is common to the Three Divine Persons, by reason of their unity of nature, and is only by appropriation attributed to the Holy Ghost. See Franz., De Trin., last Disp.; Corl., pp. 198, 199.