TEXT: Amos 2:6
"6 ¶ Thus saith the LORD; For three transgressions of Israel, and for four, I will not turn away the punishment thereof; because they sold the righteous for silver, and the poor for a pair of shoes;"
Greed is a killer. Even though Israel was a wealthy & prosperous nation, there were still those that wanted more; more to the point that they would engage in the trade of human beings, prohibited by God, practiced by the Canaanites that surrounded them. Obviously all memories of their experience of slavery in Egypt were now lost in the minds of the people, but never so in the mind of God. Again, it would be hypocritical of God to condemn those around Israel trading in the slaves but not to bring down justice on Israel for the same actions.
Ultimately, this must go back to the lessons of Egypt that seem to have been neglected. In Egypt, on the night of the Passover, there was nothing special about being a Jew that would save you. There was nothing special about being Egyptian that would condemn you. All hinged on the blood of the lamb. If you had it over the entrance to your home, you were saved. This simple lesson which was commanded that they remember, commanded that they pass it along to their children commanded that it be as frontlets to their eyes, were forgotten in Israel. Once one forgets how to ask for grace, one falls from grace.