The two most important ceremonies of the Feast of Tabernacles -pouring out of water drawn from the pool of Siloam, and the illumination of the Temple were both of post-Mosaic origin. These referred back to the water and the 'pillar of light' provided during the wilderness wandering, when people dwelt in temporary shelters. In connection with the Feast of Tabernacles John records.
John 7:37-38. In the last day (eighth day), that great day of the feast, Jesus stood and cried out, 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 heart shall flow rivers of living water.
Jesus was saying that He alone was the source of life and blessing.