is an important concept to The Church of Jesus Christ of Latter-Day Saints
. It's one of the necessary building blocks in trying to show that the Church is the only true Church of Christ
After the resurrection of Christ the Church was put into the hands of the Apostles. Due to the wickedness of the people at the time the Apostles and many of the followers of Christ's teachings were killed. Mormons believe that the Priesthood (ability to baptize and do other ordinances) must be passed down from a person holding it to another by the laying on of hands. During the Apostasy everyone with the Priesthood was either killed or died without doing this. Therefore the Priesthood no longer existed on the Earth. Things stayed this way until Joseph Smith recieved the priesthood from John the Baptist (as an angel) in the mid-1800s. Every Mormon member with the Priesthood can trace it to this event.
There is some support for this idea in the Bible. 2 Thessalonians 2:1-3:
Now we beseech you, brethren, by the coming of our Lord Jesus Christ, and by our gathering together unto him,
2 That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
3 Let no man decieve you by any means: for that day shall not come except there come a falling away first, and that man of sin be revealed, the son of perdition.
Mormons interpret this to mean that Jesus would not return until the Apostasy had taken place.
Ok, so why is this so important. If you can show that Authority of God is needed for the one true Church and that you have that Authority, then you must have the one true Church. Currently the only other religion that can really make such a claim is Catholicism by way of the passing of power from Peter (not sure on this) to the Popes. All Protestant religions need to claim that the Priesthood (if they believe in it at all) can be bestowed upon someone by faith.