The "Humans Can't Keep the Law" Narrative

One problem that I often have when I'm talking about religion with others is that they have an overarching narrative, whereas I tend to poke holes in that narrative.  For example, I know Christians who believe that the Old Testament set the stage for the New Testament.  They say that God gave Israel the law knowing that the Israelites wouldn't be able to keep it, and that would demonstrate why it was necessary for them to receive a new heart, which Jesus Christ would bring.  I would grant that, on some level, you see a similar message in parts of the Hebrew Bible.  After all, Ezekiel talks about a heart of flesh and a new heart (Ezekiel 11:19; 18:31; 36:26), Jeremiah refers to God writing God's laws on Israelites' hearts and minds (Jeremiah 31:33), and Deuteronomy mentions the circumcision of the Israelites' hearts (Deuteronomy 30:6).  But I have problems with saying that this narrative is assumed or is present throughout the Hebrew Bible.  After all, Josiah did a pretty good job in terms of obeying God's requirements (Josiah 22:2).  So did Job (Job 1:1).  So why should we assume that it's presumed throughout the Hebrew Bible that people can only fail when they attempt to obey God's law?

Did God expect for Israel to fail when he gave her the Torah?  I know someone who gave a sermon about how the Israelites were wrong at Sinai/Horeb to commit themselves to do all that the LORD said, for they should have been humbler, recognizing that they were unable to obey God's commands.  Rather than boldly proclaiming that they would do all that the LORD said, the preacher said, they should have been like the publican in Jesus' parable: crying out to God for mercy (Luke 18:13).  But let's look at Deuteronomy 5:27-29, which states (in the KJV): "[The Israelites said:] Go thou near, and hear all that the LORD our God shall say: and speak thou unto us all that the LORD our God shall speak unto thee; and we will hear [it], and do [it].  And the LORD heard the voice of your words, when ye spake unto me; and the LORD said unto me, I have heard the voice of the words of this people, which they have spoken unto thee: they have well said all that they have spoken.  O that there were such an heart in them, that they would fear me, and keep all my commandments always, that it might be well with them, and with their children for ever!"  God thought that what the Israelites said was well-spoken.  Why wouldn't this include their commitment to do all that God said?  And, when God expressed hope that the Israelites would have a heart in them to obey God's commandments, why should we assume that God is saying that they lacked such a heart on account of their sinful nature?  Perhaps God was hoping that their commitment to God would last.

But the Christian narrative (or the one I'm talking about in this post) is still tempting!  And I would even say that it's valid.  I believe that I need divine help to be good.  But I don't base that on the entire Bible having one consistent message.  On what do I base it, then?  Perhaps a number of factors: experience, as I see people become transformed when they rely on God; my personal sense of my own flaws; and maybe the message in the Bible that we can come to God for help.  So I have few problems with the narrative itself.  I largely have problems with Christians thumping their chest and acting as if the entire Bible proclaims the same message, and that those who don't agree with them are spiritually blind or are idiots.