To bear witness by the power of the Holy Ghost; to make a solemn declaration of truth based on personal knowledge or belief.

The Comforter shall testify of me, John 15: 26. He commanded us to preach and to testify, Acts 10: 42. Three witnesses shall testify to the truth, 2 Ne. 27: 12. The power of the Holy Ghost carrieth it unto the hearts of the children of men, 2 Ne. 33: 1. The scriptures testify of Christ, Jacob 7: 10-11 (John 5: 39). I testify unto you that I do know that these things whereof I have spoken are true, Alma 5: 45 (Alma 34: 8). Ye shall testify of them by the power of God, D&C 17: 3-5. That which the Spirit testifies unto you, ye should do, D&C 46: 7. I sent you out to testify and warn, D&C 88: 81.