Amos 2:6

Thus says the LORD:

"For three transgressions of Israel,
and for four, I will not revoke the punishment,
because they sell the righteous for silver,
and the needy for a pair of sandals—

Israel’s sins are her social injustice and her pagan immorality. Innocent people are cheated of justice when their judges take bribes:
They sell the righteous for silver,
and the needy for a pair of sandals (2:6).
Fathers and sons have sex with the same girls — possibly as part of the pagan fertility rites. Honour and respect has broken down in a chaos of greed and abuse.
Amos reviews Israel’s history, telling it from God’s point of view. God rescued his people from Egypt, gave them victory over their enemies and taught them what was holy. But Israel has behaved shamefully in return — commanding God’s prophets to be quiet, and getting the Nazirites (holy ones) drunk. Now God is going to crush his people with inescapable judgment. The strongest, the fastest and the bravest will all alike be overrun.

True religion
The challenge of Amos is that our worship of God should come from our hearts and affect both our personal lives and our social structures. Beautiful music and perfect offerings are nothing without the desire to treat all people fairly and the resolve to live moral and generous lives.
If we don’t offer our hearts to God when we worship him, and if we aren’t determined to change our ways, then our prayers are a pretence and our lives are a lie. Amos teaches that this angers God and provokes his judgment.

2:6. The first charge against the Israelites is that they callously sold into slavery the poor who could not pay their debts (cf. 2 Kings 4:1-7). Honest people (the righteous) who could be trusted to repay eventually, were sold for the silver they owed. The desperately poor (the needy) were enslaved because they could not pay back the insignificant sum they owed for a pair of sandals (cf. Amos 8:6). These sandals might refer to the custom of giving one’s sandals as a kind of mortgage deed or title to confirm the legal transfer of land (cf. Ruth 4:7). The meaning would then be that the poor were being sold for either money or land. Such hardheartedness against Israel’s own people, not against a foreign nation, was rebellion against God’s covenant which called for generosity and openhandedness toward the poor (Deut. 15:7-11).

After this introduction, the prophet’s address turns to Israel of the ten tribes, and in precisely the same form as in the case of the nations already mentioned, announces the judgment as irrevocable. At the same time, he gives a fuller description of the sins of Israel, condemning first of all the prevailing crimes of injustice and oppression, of shameless immorality and daring contempt of God (vv. 6–8);

Israel—the ten tribes, the main subject of Amos’ prophecies.
sold the righteous—Israel’s judges for a bribe are induced to condemn in judgment him who has a righteous cause; in violation of De 16:19.
the poor for a pair of shoes—literally, “sandals” of wood, secured on the foot by leather straps; less valuable than shoes. Compare the same phrase, for “the most paltry bribe,” Am 8:6; Ez 13:19; Joe 3:3. They were not driven by poverty to such a sin; beginning with suffering themselves to be tempted by a large bribe, they at last are so reckless of all shame as to prostitute justice for the merest trifle. Amos convicts them of injustice, incestuous unchastity, and oppression first, as these were so notorious that they could not deny them, before he proceeds to reprove their contempt of God, which they would have denied on the ground that they worshipped God in the form of the calves.

Greed, so all-consuming that for insignificant debts they would sell another into slavery (cp. Matt. 18:23–35), was accompanied by uncontained sexual passion. Care for the poor is a prominent OT theme (e.g., Prov. 14:31; 17:5) and sexual purity is mandated repeatedly. Violations of both are an affront to God’s holy name.

One cannot be right with God if he is wrong with men. When divine compassion finds no reflection in human compassion, then the altar is visited in vain.