The companionship of the Holy Ghost

2 Nephi 32: 5, 8 "the Spirit which teacheth a man to pray"
2 Nephi 33: 1 "power of the Holy Ghost carrieth it unto the hearts of the children of men."
The gift of the Holy Ghost allows us to know what we should be doing. It prompts to pray, so Man does not fall into temptation. However because a manifestation or revelation is sacred and answers to our prayers, praying provides guidance. Also, the Lord answers to prayers on His own set time. Revelations are the way Heavenly Father talks to us, which also the Lord tries us in our faith and patience.
Elder M. Russell Ballard teaches that the missionaries should be sensitive to their investigators' interests and concerns. Because missionaries need to enlighten the misunderstandings, to give encouragements, to soften the doubts and to fix up concerns, they are to find out what their investigators think and feel. Therfore, in order for them to respond to this duty, they need the companionship of the Holy Ghost, which convertsthe heart of an investigator.
It is important an investigator has the Light of Christ because it makes the investigator receive the teachings of the Gospel of Christ easier.