What's the biblical basis for the belief that God truly judges our hearts behind our actions and not the actions themselves? What's the biblical basis for the belief that God ultimately judges a thing to be a sin or not based on the intentions in our heart and not the action solely?

That would seem to be the indication in this passage, though the context of this verse is not speaking specifically of judgment of sin.


  1 Samuel 16:7 ESV But the Lord said to Samuel, “Do not look on his appearance or on the height of his stature, because I have rejected him. For the Lord sees not as man sees: man looks on the outward appearance, but the Lord looks on the heart.”




Related: https://christianity.stackexchange.com/q/45327/11471
There are many references in the bible regarding judgment however to stick to you question directly the simplest answer can be read at Jeremiah 17: 10 which states I God am the searcher of hearts examining the innermost thoughts to give each one according to his ways according to the fruit age of his works. Mt 15:19 Jesus Jesus speaks of the heart and how out of it stems many sins. And in proberbs4: 23 it counsels us to safegaurd our heart because out of it comes the source of life. So with regards to Romans 14:10 where it states we all render an account to God. Logically God knows us better than we know ourselves the psalmist states he knew us from the womb and he knows the number of hairs on our heads so from the bible I would conclude there is much more to how God judges us then simply our actions, isaiah55:8,9 says God will forgive in a large way for my thoughts are not your thoughts and your ways are not my ways declares God for as the heavens are higher than the earth so my ways are higher than your ways and my thought than your thoughts