It's all about making a choice...

Sometimes we assume that the people in the Bible had always been followers of God. But in his "farewell speech," Joshua reminds them that their ancestors, who lived on the other side of the Euphrates river, originally worshipped other gods. This makes it all the more amazing that Terah, and then later his son Abraham  (in Genesis chapters 11 and 12) heard and obeyed God's call to follow Him. They were not only heading to an unknown land, they were also following a God who was still largely unknown to them.

I suppose this is true of all of us when we first become Christians: we make our initial choice based on what others have told us about God... but then begins the journey of discovering personally what He is really like.

These people in Joshua chapter 24, however, were in a completely different situation. They had been born in the wilderness and had grown up seeing God do all sorts of miracles there.  Then, for thirty years or so, they had seen Him working in their midst and giving them great victories as they took possession of the land He had promised them. These people knew who they were dealing with, because they had experienced the faithfulness of God for themselves. They knew that not a single one of His promises to them had failed. (Joshua 23: 14)

Yet, despite this first hand experience of God,  they still had compromise and idols in their midst (vs 23). So it's to these very people that Joshua outlines life's ultimate challenge: Make a decision today about whom you're going to serve. Will it be the gods of the past, that your ancestors used to serve? Will it be gods in the future, that you see the Canaanite people serving? Or will it be the one true God, that you've experienced to be powerful and faithful in your own lives?

So the people made their choice and pledged to follow God (vs 24)... but it only lasted for a limited number of years (vs 31) - only as long as people were "personally experiencing" all that God had done for them.
You see, this isn't a decision that can be made once and then forgotten about; it truly is a decision that needs to be renewed every day of our lives, and Joshua's words still ring with urgency across the millennia: Choose today who you're going to serve.  Your whole life will be influenced by that choice.