The greatest of the religious feasts that the Jews had was the Feast of Tabernacles; it was a feast that lasted eight full days. It actually was the culmination of the feasts that preceded it in the seventh month of their calendar. The Lord waited until "the last day, that great day of the feast"—when the Jews would have had earthly religion at its highest peak and in its fullest sense—and then He cried, "If any man thirst, let him come unto Me, and drink" (vs. 37). He knew that the human heart would not be satisfied with mere religion, even if it was a God-given religion, if He were left out of it. Religion without Christ, at best, is empty religion; it only leaves the soul empty and thirsty.
The Lord's call at this time indicated that He would replace the ceremonial forms of religion in Judaism with a living relationship with Himself (Col. 2:1717Which are a shadow of things to come; but the body is of Christ. (Colossians 2:17)). He is enough to fill and satisfy the heart. This fact indicated that a dispensational change was coming. John adds (in a parenthesis) that this would take place when Christ was ascended and glorified and the Holy Spirit was given (vs. 39). These two great things characterize Christianity: a Man in the glory and the Holy Spirit sent down into this world. These are cardinal truths of the new heavenly order in the Dispensation of grace. Christ in the glory is the center of God's new program; it is not Christ on earth, as in the old dispensation. Christ would be the Object of the believer's focus; the Holy Spirit dwelling in believers would be the power by which the new joys of Christianity would be possessed and enjoyed.
Moreover, this new order of blessing was so great that it could not be confined to Israel; hence, the Lord says, “If any man....” This heavenly order of blessing would be available to all—even Gentiles who would believe.