In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)

John 7:37-39

On the last day of the Feast of Tabernacles, the Jews had a custom of drawing water from a well reminding them of the water that Moses brought from the rock in the wilderness. The leaders foolishly said that this also represented how they drew the spirit of God into their presence. This practice shows their predisposition saying that they are made holy by outward works and signs.

Jesus sets them straight!

The rock in wilderness represented Jesus and the water is the Spirit but it flows from Jesus inside the born again person. 

And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.

1st Corinthians 10:4

The source of spiritual life does not come from outward conformity to laws, ceremonies, or traditions. Spiritual life is imparted at the new birth by the power of God. Further, the gift of the Spirit (which is what is under consideration here) cannot be conjured up by prayer, ceremony, or ritual. On the day of Pentecost, we find this promise being fulfilled when the gifts of the Holy Spirit are made manifest in tongues, healings, prophesying, etc. 

This was promised in various places in the Old Testament but very clearly in Joel. Notice that even in the promise of the gifts, it is GOD imparting the gift of His spirit by His power not by man’s will, action, or ceremony.

And it shall come to pass afterward, that I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions:

Joel 2:28

All of the events in John, Chapter 7 have been pointing at the same thing — The law does not justify, sanctify, or save in any way. All the works of the law and its ceremonies were pointing to Jesus Christ. Who is the only source and cause of salvation.

But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption: That, according as it is written, He that glorieth, let him glory in the Lord.

1st Corinthians 1:30-31

What a wondrous gift we have in Jesus Christ! He has done it all so let us glory in Him and Him alone!