In Hebrews 3:12, the apostle Paul reports of Israel's "evil heart of unbelief," the fountain, the source, that gave birth to her irrational, erratic, unreliable spiritual and moral behavior. She could not be trusted to remain firm to her commitment to be faithful in keeping the commandments and thus God's way of life. Had the making of the covenant been a literal marriage between two humans, her conduct would have been as God called it, harlotry. However, this was an agreement between a holy, spiritual God and the human nation He chose.
Though she transgressed every commandment in multiple ways, collectively, the spiritual sin through which her unfaithfulness is most frequently demonstrated is gross idolatry. Israel simply serves herself, following the whim of the moment, so that she might "have fun." Her lack of belief grants her nature free rein to exhibit itself in the self-endowed liberty to follow the lust of her flesh, the lust of her eyes, and the pride of life. She rejects her divine Husband as her Ruler because she wants a king "just like" the other nations.
Except for the occasional times when Israel had good leadership, she conducted her affairs, whether personal, domestic, or international, in the Babylonian manner. Israel, despite her great advantages, became just another kingdom of this world. While God has remained faithful to His agreements and promises through the centuries, she has maintained a hypocritical "God's people" stance toward the world, palming herself off as a "Christian nation."
With the founding of the church following Christ's resurrection, God's spiritual focus turned to the church. Having made the New Covenant with God, our charge now is to be faithful while living surrounded by Babylon the Great. Though it is literally physically impossible, we have the responsibility to come out of her, and we can come out spiritually by being faithful to God and His commandments. We must not fail as Israel did, for the stakes for us are much greater. The New Covenant is a better covenant than Israel made; it contains better promises, enabling us a much better opportunity to be faithful and grow. However, those greater advantages also render us more responsible than even Israel, God's only chosen nation, because the church of God is God's only chosen church.