A cursory reading of the Jewish Scriptures reveals that YHWH is concerned about two primary topics. The first is Israel's fidelity to Him. It was YHWH who called Abram and YHWH who called Israel from Egypt. Finally, it was YHWH who had mercy on Israel and brought her from exile in Babylon. There are a number of reminders of these realities throughout the Jewish Scriptures. He has been faithful to Israel and He expects she would be faithful to Him. Fidelity then is one topic that is recurring in Jewish Scriptures.
The second recurring topic is the kind of people Israel was supposed to be. The expectation is that they would reflect their God, His character in their relationships with each other. Of particular importance to YHWH is the behavior of Israel's leaders - her kings, prophets, judges, and other organs of the state. The behavior of the populous is as important, but the maladies affecting Israel are routinely placed at the feet of those in power.Two recurring themes fidelity and character. When YHWH sends Israel off into captivity and then on His own initiative, elects to redeem her, to reconcile her to Himself, the constant refrain is that Israel will once again be faithful to YHWH and will be shaped into people who reflect His own character.
What is this character that Israel is to reflect? Micah gives us a hint when he offers, to act justly and to love mercy. Justly here does not mean justice in a legal, objective sense, but fairness coupled or tempered with mercy. To treat someone justly does not mean to execute justice and throw them in jail. It means to bear with them, to not take advantage of them. It means to give them their due. Justice we are told was often perverted in Israel to the benefit of the powerful and sly. As a result, the poor were taken advantage of and abused by the very people they should be able to trust. They were not being treated justly. Mercy then tempers and shapes our treatment of others in the direction of healing, of reconciliation, of life. Mercy foregoes my prerogatives for your benefit.
Isaiah's description of the fasting that YHWH likes is not simply self denial, but self denial that issues in the benefit of others. Mercy and justice. These two are the common themes when YHWH complains about Israel's character. It seems that YHWH could almost bear with the high places but for the failure of Israel to assume His character in their lives with each other. The greatest surprise for YHWH is not that Israel would worship Moloch, but that they would feed their children to him.The abuse of others, the lack of YHWH character in His people seems the greater form of infidelity. Having been created as a nation at His discretion, that He has demonstrated steadfast love for her should have resulted in their steadfast love for each other. It resulted in their abandonment of Him and the further deterioration of their own lives and character. There seems to be no limit to our possible depravity when we focus on ourselves and on gaining more and more for me and mine.
Those who would be the people of God are expected to assume YHWH's character and this is the measure of whether those people are indeed His people. The honoring and worship of YHWH is expected by Israel as a starting point; as a basic understanding of Him as the God for His people. But this acknowledgement isn't sufficient. We are reminded that even the demons believe but we are not at all assured that those demons are "saved." Acknowledgement of God or even destroying the high places is not what God is after entirely. Rather, after we acknowledge God, it has always been necessary to live like Him - as His image and likeness.