Joseph Smith was asked if he believed himself "to be a Prophet?" His reply was:
"Yes, and every other man who has the testimony of Jesus. For the testimony of Jesus is the spirit of prophecy" (TPJS, p. 119; also Rev. 19:10).
Possessing "the testimony of Jesus" is more than we think it is. "Testimony" is so common a thing among us we think we understand the phrase "testimony of Jesus." Merely saying you know Christ lives or loves you, doesn't mean you possess the testimony of Jesus spoken of by John and Joseph. We read that even the devils possess that testimony (James 2:19; Matt. 8:29). Therefore, declaring that Jesus is Christ, even if you know such is the case, is not what is meant - though that may be where it begins.
Latter-day Saints aren't the only churchgoers who have such a testimony. There are believing Christians everywhere that believe in and serve the same Christ we proclaim we know. Yet, Jesus said:
"Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
"Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
"And then will I profess unto them, I never knew you: depart from me, ye that work iniquity" (Matt 7:21-23).
Those Christ spoke of, who thus testified, had not the "testimony of Jesus," and will not "enter into the kingdom of heaven." Though they believed they pleased him with their "wonderful works," they were workers of "iniquity" according to Christ. These are the churchmen, not the prophets. These are those who are religious, but who know not the mind and will of God. They are "professors," and are all corrupt (JSH 1:19). Their creeds are an abomination to God (ibid.). They are led in masses to believe they are correct, but their hearts are far from God. They have entered in at the "broad gate," and many there be that go in thereat (Matt. 7:13). They belong to the telestial kingdom (D&C 76:99-101).
We should pause to consider what the Lord is saying here. How is it that those Christ spoke of believed they did "wonderful works" but did not "the will of the Father?" How is it that they thought they "prophesied in [his] name" but weren't found pleasing to God? How is it that they "cast out devils" but were called workers of "iniquity?" What is this "testimony of Jesus," and how does it differ from testifying that you have done "wonderful works" and saying "Lord, Lord."
Prophets and prophetesses are a different type of people than the religious who only profess to know Christ. They are unlike the masses. Historically, the prophets did not please the majority. Words like "anger," and "offended" are used in scripture to denote the reaction of the people to their message (3 Ne. 6:20-21; Matt. 15:12). "Mad," and "wild" are used by the religious to describe their demeanor (Mosiah 13:1; Moses 6:38). And yet, these are they who possessed the "testimony of Jesus." How could this be?
The testimony of Jesus is more than just your testimony. It is His testimony. It is you receiving Jesus' testimony to you. What is it that Jesus would testify of were he to give you his testimony? Do we begin to learn about this at all in the temple?
What is it about what Christ makes of these men that is so offensive to those who consider themselves God's chosen people? Why is Zion so rarely established, when God has given men opportunities to establish it?
Salvation requires revelation. This is not only true for every individual that is to be saved, but also for those who preach the gospel of salvation. It is vain for a man to attempt to minister without it (TPJS, p. 160). Prophets preach Christ's gospel, and minister to others with power because of the revelations they receive (ibid.). Prophets have the testimony of Jesus, and possess the gift of the spirit of prophecy. They encourage others to receive the same.
Our revelations indicate that there are those who claim to be apostles and prophets, but whose falseness and hypocrisy shall be uncovered when Zion is established (D&C 64:38-39). What does that mean? The Prophet taught that false prophets will testify of heaven and hell, but they have seen neither (ibid.). True prophets, who receive their message from God, always point to Christ and never set themselves up for a light unto others. They teach that unless men repent and come unto Christ, they are lost (1 Ne. 10:5-6).