The Dew From Heaven
Deuteronomy 18:18-22 is often quoted as the test for a prophet.
"I will raise them up a Prophet from among their brethren, like unto thee, and will put my words in his mouth; and he shall speak unto them all that I shall command him. And it shall come to pass that whosoever will not hearken unto my words which he shall speak in my name, I will require it of him. But the prophet which shall presume to speak a word in my name, which I have not commanded him to speak, or that shall speak in the name of other gods, even that prophet shall die. And if thou say in thine heart, How shall we know the word which the Lord hath not spoken? When a prophet speaketh in the name of the Lord, if the thing follow not nor come to pass, that is the thing which the Lord hath not spoken; but the prophet hath spoken it presumptuously; thou shalt not be afraid of him."
The Lord said that he would destroy all life on earth, but then changed his mind.
"And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them." (Genesis 6:7)
The Lord told Ezekiel, that the City of Tyre would be destroyed, and swept clean, and never rebuilt (Ezekiel 26), but Tyre exists to this day.
The true test of a prophet is not whether a prophecy comes to pass. Prophecies are often conditional. The mere act of giving a prophecy can change it.
At what instant I shall speak concerning a nation, and concerning a kingdom, to pluck up, and to pull down, and to destroy it; If that nation, against whom I have pronounced, turn from their evil, I will repent of the evil that I thought to do unto them. And at what instant I shall speak concerning a nation, and concerning a kingdom, to build and to plant it; If it do evil in my sight, that it obey not my voice, then I will repent of the good, wherewith I said I would benefit them. (Jeremiah 18:7-10)
The true test is whether the prophet is associated with signs, wonders, miracles, and the gifts of the Holy Ghost. These are the fruits of a true prophet.
"How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him; God also bearing them witness, both with signs and wonders, and with divers miracles, and gifts of the Holy Ghost, according to his own will?"
(Hebrews 2:3-4)
A prophet is somewhat an honorary title given to someone who speaks for God, or through whom God can speak. They can also speak for themselves, so not everything they say comes from God. Prophets are known for their wisdom, wisdom that seems beyond the knowledge of mankind. They are also known for miracles, although they are the first to admit that the miracles come from God. They are most well known for what they do the least; prophecy of future events.
"Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit;"
(Ephesians 3:5)
Continued Reading: What is a Miracle?