A testimony is what the Savior was talking about when He told Peter, “Flesh and blood hath not revealed it unto thee, but my Father which is in heaven” (Matthew 16:17). It is knowledge from God revealed through the Holy Ghost.
The Holy Ghost speaks in a voice we feel more than we hear, but it comes both “in your mind and in your heart” (Doctrine and Covenants 8:2; emphasis added)—our thoughts as well as our feelings.
The Prophet Joseph Smith described the spirit of revelation as a feeling of “pure intelligence flowing into you, [giving] you sudden strokes of ideas” (Teachings of Presidents of the Church: Joseph Smith , 132).
When we turn our minds and hearts—our thoughts, feelings, and desires—to God, He can speak to our minds and hearts with the still, small voice of the Holy Ghost. As He engages our spirits, certain feelings and thoughts seem to flow to us. This is the testimony He gives us.