I certainly understand this sort of thinking; it comes from the old performance mentality, the same old lies that say, "you're OK only until you mess up; then you're irredeemable." We think we can pass the audition but if we miss our cue or flub our lines, an understudy will take over and we'll be thrust out the backstage door into the outer darkness, where there is weeping and gnashing of teeth.
But wait, you say, that's true, isn't it? If the star of the show shows up drunk or something and can't perform, the understudy takes over, yes?
Let's have a look at where this verse comes from to see why I think God's plan is not like a play or concert or opera performance. The passage is in Jeremiah 29; it's part of a letter to Israelites living in Babylon. These people are in Babylon because the nation has not obeyed the Lord -- Israel was full of violence and greed and idolatry. In other words, the plans to prosper the Israelites, to give them hope and a future, were announced after they disobeyed the Lord for generations—hundreds of years of disobedience! And yet he says, "I know the plans I have for you," declares the Lord, "plans to prosper you and not to harm you, plans to give you a hope and a future. Then you will call upon me and come and pray to me, and I will listen to you. You will seek me and find me when you seek me with all your heart." (Jeremiah 29:11-13)
Hundreds of years of disobedience by millions of Israelites didn't thwart God's plans for their nation, and yet we worry that a few decades of disobedience by one individual might lead him to break his promise. As if we could disappoint him so much in a way he didn't already know!
I mean, did God say "Before a word was on your tongue, I knew it completely (Psalm 139) but then you came out with that??" Or "Before I formed you in the womb I knew you (Jeremiah 1) but then you went and did something else." Or "I chose you in Christ before the foundation of the earth to be holy and blameless (Ephesians 1) but then you went and messed it all up."
I don't think so. As I wrote last month, God already knows (Isaiah 44:6-7, 46:10) what will happen; there is no way that we can surprise or disappoint him, and there is no way that he will change his mind about his plans. He doesn't do that.
And isn't that good news?