Note: As the Church has said, the manual has been prepared as the primary source of lesson material. These supplements, from general conference addresses, are meant only as a complement to your study on this lesson’s topic.
Supplement is from Elder Dallin H. Oaks's talk, "Testimony" from the April 2008general conference:
What do we mean when we testify and say that we know the gospel is true? Contrast that kind of knowledge with “I know it is cold outside” or “I know I love my wife.” These are three different kinds of knowledge, each learned in a different way. Knowledge of outside temperature can be verified by scientific proof. Knowledge that we love our spouse is personal and subjective. While not capable of scientific proof, it is still important. The idea that all important knowledge is based on scientific evidence is simply untrue.
While there are some “evidences” for gospel truths (for example, see Psalm 19:1; Helaman 8:24), scientific methods will not yield spiritual knowledge. This is what Jesus taught in response to Simon Peter’s testimony that He was the Christ: “Blessed art thou, Simon Bar-jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven” (Matthew 16:17).