"It is also written in your law, that the testimony of two men is true. I am one that bear witness of myself, and the Father that sent me beareth witness of me." (John 8:17-19)
There are two witnesses. Jesus testified that he was one, and that the Father is the other. The Father because he is the word. The Son because he attained unto the word.1 The Son showed it is possible and it is the testimony of Jesus, in other words, the works of God2 demonstrate to us what is required to be just and true.3
One witness is truth, the other witness is the truth and demonstrability of the first.
The Holy Ghost is not a witness to us, but technically is the means by which we receive these two witnesses4, yet it can become a third witness to others. Three degrees of Glory, three witnesses, each ministering to their own sphere.
1. "In the beginning was the gospel preached through the Son. And the gospel was the word, and the word was with the Son, and the Son was with God, and the Son was of God." (John 1:1, Inspired Version)
2. "And he ministered unto him even as he ministered unto the Nephites; and all this, that this man might know that he was God, because of the many great works which the Lord had showed unto him." (Ether 3:18)
3. "For if we can find a saved being, we may ascertain, without much difficulty, what all others must be, in order to be saved—they must be like that individual or they cannot be saved: we think, that it will not be a matter of dispute, that two beings, who are unlike each other, cannot both be saved; for whatever constitutes the salvation of one, will constitute the salvation of every creature which will be saved: and if we find one saved being in all existence, we may see what all others must be, or else not be saved. We ask, then, where is the prototype? or where is the saved being? We conclude as to the answer of this question there will be no dispute among those who believe the bible, that it is Christ: all will agree in this that he is the prototype or standard of salvation, or in other words, that he is a saved being. And if we should continue our interrogation, and ask how it is that he is saved, the answer would be, because he is a just and holy being; and if he were any thing different from what he is he would not be saved; for his salvation depends on his being precisely what he is and nothing else; for if it were possible for him to change in the least degree, so sure he would fail of salvation and lose all his dominion, power, authority and glory, which constitutes salvation; for salvation consists in the glory, authority, majesty, power and dominion which Jehovah possesses, and in nothing else; and no being can possess it but himself or one like him" (Lecture on Faith, 7th)
4. "There are two personages who constitute the great, matchless, governing and supreme power over all things—by whom all things were created and made, that are created and made, whether visible or invisible: whether in heaven, on earth, or in the earth, under the earth, or throughout the immensity of space—They are the Father and the Son: The Father being a personage of spirit, glory and power: possessing all perfection and fulness: The Son, who was in the bosom of the Father, a personage of tabernacle, made, or fashioned like unto man, or being in the form and likeness of man, or, rather, man was formed after his likeness, and in his image;—he is also the express image and likeness of the personage of the Father: possessing all the fulness of the Father, or, the same fulness with the Father; being begotten of him, and was ordained from before the foundation of the world to be a propitiation for the sins of all those who should believe on his name, and is called the Son because of the flesh—and descended in suffering below that which man can suffer, or, in other words, suffered greater sufferings, and was exposed to more powerful contradictions than any man can be. But notwithstanding all this, he kept the law of God, and remained without sin: Showing thereby that it is in the power of man to keep the law and remain also without sin. And also, that by him a righteous judgment might come upon all flesh, and that all who walk not in the law of God, may justly be condemned by the law, and have no excuse for their sins. And he being the only begotten of the Father, full of grace and truth, and having overcome, received a fulness of the glory of the Father—possessing the same mind with the Father, which mind is the Holy Spirit, that bears record of the Father and the Son, and these three are one, or in other words, these three constitute the great, matchless, governing and supreme power over all things: by whom all things were created and made, that were created and made: and these three constitute the Godhead, and are one: The Father and the Son possessing the same mind, the same wisdom, glory, power and fulness: Filling all in all—the Son being filled with the fulness of the Mind, glory and power, or, in other words, the Spirit, glory and power of the Father—possessing all knowledge and glory, and the same kingdom: sitting at the right hand of power, in the express image and likeness of the Father—a Mediator for man—being filled with the fulness of the Mind of the Father, or, in other words, the Spirit of the Father: which Spirit is shed forth upon all who believe on his name and keep his commandments: and all those who keep his commandments shall grow up from grace to grace, and become heirs of the heavenly kingdom, and joint heirs with Jesus Christ; possessing the same mind, being transformed into the same image or likeness, even the express image of him who fills all in all: being filled with the fulness of his glory, and become one in him, even as the Father, Son and Holy Spirit are one." (Lectures on Faith, 5th)
I invite you to ponder and see if the Holy Spirit does not manifest something to you. Don't accept anything because I say it, but only consider it, and see if in the future, the Holy Ghost witnesses.
My previous article: The Holy Spirit