Joshua 21:45 There failed not ought of any good thing which the LORD had spoken unto the house of Israel; all came to pass.
This sentence could be placed almost anywhere in history. It is true. God keeps His Word. Not one thing that He had promised failed to come true.
There are still promises to be fulfilled. There are still things that are going to happen. You can be certain that what He says will happen. He is trustworthy.
So as you read the Bible if you see a promise that hasn’t happened yet then you can know that it is a prophecy. A promise of future blessings. It will happen. All that He says happens. He is almighty God. He is trustworthy!