As a personage of spirit, the Holy Ghost can be in only one place at a time, but His influence can be everywhere at the same time.
President Joseph Fielding Smith taught, "Through the Holy Ghost the truth is woven into the very fibre and sinews of the body so that it cannot be forgotten."
It is also through receiving the Holy Ghost when we repent and are baptized that we may be sanctified. Sanctification is the process of becoming free from sin—pure, clean, and holy— through the Atonement of Jesus Christ (see Moses 6:59-60). We are sanctified as we yield our hearts to God (see Helaman 3:35).
taken from March 2010 Ensign Magazine