See Acts 2:1 and note. The Feast of Pentecost was the feast of the fiftieth day, counting from the day after the Sabbath, the day on which the sheaf of the wave offering was brought to God (v. 11), to the day after the seventh Sabbath (v. 15). This signifies the resurrection of Christ in its sevenfold fullness reaching the realm of the complete fullness, bearing the full responsibility, signified by the number fifty (composed of ten times five, ten signifying fullness and five, responsibility), for the testimony of resurrection.
On the day of Pentecost in the New Testament, the consummation of the Triune God — the all-inclusive, life-giving, compound Spirit of the processed Triune God, who is the totality of the Triune God — was poured out upon the one hundred twenty disciples as representatives of the Body of Christ. As a result of such an outpouring of the economical Spirit of God, the Body of Christ came into existence as the increase, the enlargement, of the unlimited, individual Christ, making Him the universal, corporate Christ (1 Cor. 12:12-13), the mingling of the processed and consummated Triune God with His chosen and redeemed people, which will ultimately consummate in the New Jerusalem.