One of the greatest promises it makes is to send us a Comforter. Jesus says this to his Apostles on his last night of mortal life.
"Comforter" has a lot of significance for us in modern times. With all the stress and dissonance in modern life, one thinks of a comforter as a counselor or a friend in times of need, a shoulder to cry on. Another meaning for it is a warm blanket one keeps folded until needed.
Comfort fills a need, but the most interesting thing about the Comforter that Christ mentioned is that it fills a need that most people don't realize they have, though so many are aching for it. It is the need for a connection to God.
The Comforter is actually the Holy Ghost, and it was os important that it be given to the early Church upon Christ's Ascension because it would allow the Church to grow and aid member's souls through revelation and assurance. In the 1st Century, both Jews and Christians were harassed and murdered. Members of the Church today don't usually encounter that problem, but the significance and need for the gift of the Holy Ghost is just as important. Satan's efforts to confuse and destroy are even more forceful than the efforts of the Jewish Sanhedrin and the Roman Empire to destroy the Primitive Church.
The gifts of the Spirit are vast and endowed with force by God's grace when the gift of the Holy Ghost is given by confirmation. This gift is immeasurable, and unending.