A prophecy is simply an inspired utterance from the Spirit of God through a vessel he chooses. Prophecy can be in the form of forthtelling( exhortative) or foretelling( predictive). The latter comes to mind when most of us hear the word "prophecy". 
My focus is simply on the counsel of Paul to the brethren in Thessalonica. He counseled that they should not scoff at prophecies. To scoff at prophecy is to despise it and make light of what God is saying. On several occasion, I have seen this happen. The resultant effect is not always good.

I used to know an evangelist who was burning for the Lord. When it was time to marry, the word of the Lord came to him through a trusted and tested vessel that he shouldn't marry the lady he wanted to marry. He scoffed at the prophecy and he responded by saying: "We'll stop evil with prayers".

This man eventually married the lady but he is no more as I speak. Before his death, his church ran down, his wife became promiscuous. The last we heard of her was that she married an "Alhaji". The ministry of that man wrecked. Why? He scoffed at prophecy. I believe it wasn't God'd will for him to die.

Instead of scoffing at prophecies, in the next verse, Paul counseled: "BUT TEST EVERYTHING THAT IS SAID. Hold on to what is good". This is what I think we should do. It is the scriptural way to go.

When God sends a word of prophecy to you either exhortative or predictive, your primary duty is to take it to God's laboratory for testing. It is your scriptural right to test every "thus saith the Lord" that comes to you. You can search for my teaching on the subject via this link: https://www.facebook.com/share/1ZUAzG1BhU/

Every word from God is for your benefit. It might be to prepare you for what is ahead or to warn you against the plans of the enemy.

In the time of Noah, they were warned about the flood but the people of his time scoffed at his prophetic warning. They became victims of his warnings. Jonah, through prophetic insight warned the people of Nineveh and they repented. God's anger and judgement was reversed. The choice is yours.