Deuteronomy 32:5
They have corrupted themselves, their spot is not the spot of his children: they are a perverse and crooked generation. They have corrupted themselves, their spot is not the spot of his children: they are a perverse and crooked generation.
This belongs to a sacred song recounting God's dealings with His people, commanded to be formed so that Israel could teach its children and keep the history of God's work in remembrance, and looking ahead prophetically to the final victory of the faithful when Christ comes again in power and glory. It means the people have corrupted or spoiled themselves, that their spot or stain is not that of His children, and that they are a perverse and crooked generation, unfaithful in character and unlike God's children. That corrupt character stands in contrast with God, whose work is perfect and whose ways and character are truthful, just, right, and righteous. It exposes the guilt of those who receive great light and love yet fail to respond with gratitude and obedience.
In the setting of Judah's apostasy it identifies the sin as rebellion, that Israel had departed from God and failed to honor His name with outward religious ceremonies taking the place of a renewed heart, and it introduces the account of their idolatry. People corrupt themselves by acting contrary to God's principles, by taking up truth without being converted to practice it so they retain old characters, mix their own spirit into counsel and actions, and misrepresent God. Their spirit, words, and actions do not show love for God and keeping of His commandments, and the character thus cultivated in daily life and relationships is what is brought forward.
It warns of judgment for those who persist in this course, with character brought into the judgment and corruption bringing the declared judgment including captivity and the destruction of the Temple and the end of its services, while faith in Christ and obedience to His words mark those united with Him.