Alma 5

I have always been touched by the testimony given by Alma to the people of Zarahemla. That's because it is the same testimony I have. What is significant is that Alma had already experienced a resounding visit by an angel, but here he shares why he really knows these things are true as he asks -

"... Do ye not suppose that I know of these things myself?..." (Book of Mormon | Alma 5:45)

You would expect that he knows because he was visited by and angel, but instead answers -

"...Behold, I testify unto you that I do know that these things whereof I have spoken are true. And how do ye suppose that I know of their surety?
46 Behold, I say unto you they are made known unto me by the Holy Spirit of God. Behold, I have fasted and prayed many days that I might know these things of myself. And now I do know of myself that they are true; for the Lord God hath made them manifest unto me by his Holy Spirit; and this is the spirit of revelation which is in me." (Book of Mormon | Alma 5:45 - 46)

And then he adds to his testimony -

"...moreover, I say unto you that it has thus been revealed unto me, that the words which have been spoken by our fathers are true, even so according to the spirit of prophecy which is in me, which is also by the manifestation of the Spirit of God.
48 I say unto you, that I know of myself that whatsoever I shall say unto you, concerning that which is to come, is true; and I say unto you, that I know that Jesus Christ shall come, yea, the Son, the Only Begotten of the Father, full of grace, and mercy, and truth. And behold, it is he that cometh to take away the sins of the world, yea, the sins of every man who steadfastly believeth on his name." (Book of Mormon | Alma 5:47 - 48)