2 Kings 20:1-11. Isaiah the prophet gave God’s word to King Hezekiah.
King Hezekiah got ill and Isaiah had said he would get better. The King asked for proof. Isaiah said King Hezekiah do you want the shadow of the sun to go forward ten steps or back ten steps. King Hezekiah replied to the prophet Isaiah for the shadow go back the ten steps it had gone down on the stairway of Ahaz.
Hezekiah’s Illness
2 Kings 20:1 During this time, Hezekiah became sick with a fatal illness, so Isaiah the prophet, the son of Amoz, approached him and told him, “This is what the LORD says: ‘Put your household in order, because you are dying. You will not survive.’” …Now Hezekiah had asked Isaiah, “What is to be the sign that the LORD is healing me and that I’ll be going up to the LORD’s Temple three days from now?”So Isaiah replied, “This will be your sign from the LORD that the LORD will do what he has promised. Shall the shadow go forward ten steps or go back ten steps?”Hezekiah answered, “It’s an easy thing for a shadow to lengthen ten steps. So let the shadow go backward ten steps.” So Isaiah cried out to the LORD, who brought the shadow back ten steps after it had gone down the stairway of Ahaz.
The shadow
I don't know what is causing the shadow. I don't think it matters too much. For this answer I will assume that the steps are literal, and the shadow is a building or some other structure.
To move a shadow you must move either the light source, or the object blocking the light source (or both). The object making the shadow has the part of the top fall off, and this makes the shadow go back 10 steps. This, to me, is the simplest solution.
This is an explanation for the phenomenon however what is important to note is not how it happened but that this was the word of the prophet and it confirmed the Word of God to the King.
Prophetic confirmation
There were likely a number of false prophets around at this time (e.g. Isaiah 44:25). Perhaps in asking for a sign Hezekiah was trying to ensure the truthfulness of the prophecy (and prophet).
2 Peter 1:19a: Moreover, we possess the prophetic word as an altogether reliable thing.
We surely need confirmation for every prophetic word we receive. If the word comes through a prophecy or whether you hear God’s voice directly you will need confirmation.
How to Respond to a Prophecy?
You’ve just heard a prophecy. It could have been a personal prophecy, or a word from the Lord delivered corporately, or to a group of people. Either way, you are now in possession of a message from God. So, what do you do now?
1. Identify the prophets (true or false)
2. Words that come through prophetic utterance are not to be taken lightly.
“Do not scoff at prophecies!” (1 Thessalonians 5:21)
When you hear a prophecy, you can’t sit back and wait for it to happen. There is something you need to contribute to keep it moving along—praying, declaring and standing in faith for that word to come to pass.
The sun went backwards