The Comforter

John chapters 15-16 speak of Comforter that Christ will send. Here is one of the first biblical descriptions of the mission of the Holy Ghost that we see in the New Testament. As a member of the Godhead the Holy Ghost has a very important role among mankind, and can manifest himself with great power. This is seen in the event of the Pentecost, however while this may be the most famous of His manifestations, it is not the most important role.
Christ gives us the significance of the Holy Ghost's most important mission in the Gospel of John. This great mission of the Holy Ghost is found in 15:26 " But when the Comforter is come... which proceedeth from the Father, he shall testify of me"
It is this reassuring witness, that not only speaks for itself, but also witness for the Father, that is true comfort for the humble followers of Christ. Knowing that you are doing the right thing despite all the disparagement that world will throw at you is why Christ sent the Holy Ghost to us.
Christ also spoke of the Comforters other missions, that of purging us from sin, and being a guide and a teach to us since Christ is with the Father and can not be with us always.
The Comforter is the supreme teacher of the Truth of God and will reveal to us all the mysteries of godliness, in verse 13 it reads " he will guide you into all truth... and he will shew you things to come.
It is this revelation and continuing teaching that Joseph Smith will expound on in helping us to understand how to receive the Second Comforter, which is Christ himself, for we are purified and tutored by the Holy Ghost we can become ready for that glorious day.