How do we know that we cannot keep God's law?

From the Old Testament, particularly in Deuteronomy 29, we see the call to keep the entire law and recognize the consequences of failing to do so. Humanity, represented by Israel, is depicted as unable to fulfill the demands of the law. The text highlights that the Lord has not granted them the heart, eyes, or ears necessary to perceive the truth, indicating that apart from divine intervention, we remain blind to our inability. Romans 3 reinforces this by asserting that all have sinned and fall short of the glory of God, echoing the impossibility of achieving righteousness through our own efforts.