Deuteronomy 7:9 Therefore know that the Lord your God, He is God, the faithful God who keeps covenant and mercy for a thousand generations with those who love Him and keep His commandments;
An idol cannot show mercy and faithfulness; but they can sit there and do absolutely nothing when you want them to!
God made promises to mankind in the beginning. God made promises to Israel. God made promises throughout history. And God keeps those promises!
We fall short, we give in, we bend the rules, we take short cuts and we still know God is willing to forgive and take us back!
A thousand generation is a very long time and this passage reminds us we are limited in time, but God is not!