This test is only necessary if He intends to send prophets. The test is given so you may identify both true and false prophets. Implicit in this, is the obligation to personally account for your response to those He sends, and those who claim to be sent by Him. You must choose. Your choice will count for and against you. You must grow to apply the test correctly.
The concept of "sheep's clothing" is worth pondering. Why is it even possible for such a thing as "sheep's clothing?" Think about it. The attire or mantle they pretend to possess is necessarily "sheep-like" to the casual observer. That is, the "office" or the position or conduct or credentials of the false prophet must be misleading. They should appear bona fide. They need to seem authentic.
Now, lest you be confused about the "wolves" who occupy these positions, it does not mean an utterly corrupt, completely perverse man. It only requires the "wolves" to be unable to deliver a true message from the Lord. It only requires that they not be sent with an authentic message from Him. They must pretend to be His, but He has nothing to do with their message.
So, how are we to distinguish between the "sheep" and the "wolves" who come as "prophets" from the Lord? In a word, it is the "fruit." What does the message produce?
A false prophet's message will produce as its fruit vanity, corruption, evil, foolishness, arrogance, self-assuredness, error, distance from the Lord, poor understanding, popularity, wealth, success, ease, false hopes, ingratitude, pride, displays of popularity, worldliness, hard hearts and ten thousand other meaningless or deceptive fruits.
A true prophet's message will produce repentance.
The only good fruit which can be offered in this world is repentance. When mankind lays down their sins because of a message, that message comes from Him. All others are distractions and invite you to err. The fruit which gives eternal life is repentance and a return to Christ.
When the message comes from a false prophet, you can know the messengers, along with those who listen to it, and the message itself will be "hewn down, and cast into the fire." It will be purged.
When the message comes from a true prophet, you can know the message, along with those who heed it, and the messenger will survive the burning which is to come, because they are purged by repentance and can abide the day of wrath.
Few there be that find it, indeed.... It needn't be so. But as Joseph Smith commented: "The world always mistook false prophets for true ones, and those that were sent of God, they considered to be false prophets, and hence they killed, stoned, punished and imprisoned the true prophets, and these had to hide themselves ‘in deserts and dens, and caves of the earth’ (Heb. 11: 38), and though the most honorable men of the earth, they banished them from their society as vagabonds, whilst they cherished, honored and supported knaves, vagabonds, hypocrites, impostors, and the basest of men." (DHC 4: 574.)
I suppose that will always be the case. However, we have a guarantee the President of The Church of Jesus Christ of Latter-day Saints is unable (and will always be unable) to lead us astray. It is little wonder we cherish, honor and support that office as we do; preferring it even above scripture. (See Fourteen Fundamentals for Following the Prophet, Ezra Taft Benson, BYU Address February 26, 1980; the second fundamental; recently spoken of in our last General Conference.)