If what God says to you in a vision is different to what is in the Bible, how can you trust it? And if it is in the Bible, why would you need a vision????
And another question is...
Why does God give visions when He has already given us His Word?
In the Old Testament and a few times in the New Testament, God spoke to people in visions or dreams. I remember thinking one time, “Why do all the dreams in the Bible mean something and yet dreams today don't? I sure wouldn't want all my strange dreams to have meanings!!” And then I realized that back then people didn't have the whole Bible to read like we do today.
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
That the man of God may be perfect, throughly furnished unto all good works. 2 Timothy 3:16-17
God tells us how He speaks to us today.
God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets,
Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds; Hebrews 1:1 -2
Then these verses in John say that Jesus is the Word. So God speaks to us by His Son, through the Bible—God's written Word.
John 1:1,14 In the beginning was the Word, and the Word was with God, and the Word was God. And the Word was made flesh, and dwelt among us, (and we beheld his glory, the glory as of the only begotten of the Father,) full of grace and truth.
Many cults have started because of their leaders having visions and believing God spoke to them.
They each believe they are they are the right group and yet their beliefs contradict each other and the Bible. Yet if God truly spoke to each of them, this wouldn't happen.
I found this list of several things that are common with people who have visions. The person who made this list had met many people who had visions. I thought it was interesting as it makes it quite obvious to me that the visions aren’t from God!
1) They have been thinking about the subject of the vision before it happened or something else triggers the dream.
2) It often happens in relationship to sleep. The person wakes up and has the vision.
3) The vision generally confirms to them what they had already been thinking about.
4) The vision generally does not bring them closer to the Lord, but directs them away from the Bible and/or sound doctrine.
5) Without exception the person who has the vision was in doctrinal error and/or attending a church that was doctrinally unsound.
I hope this is helpful! But above all, pray that God will give you the right words. He knows exactly what that person needs.