In this section of his book Amos relates the message given to him by the Lord regarding what he would do about the sins of his people. The first detail may surprise us -- the Lord calls for two pagan groups, one from the Philistia and one from Egypt, to witness the sinful practices of his people (3:9). This invitation may have been a rhetorical one used by the prophet to inform his hearers that their practices were worse than what those foreigners would have seen in their own countries.
Amos informs the Israelites that they will be defeated by a foreign army. This scenario seemed unlikely at the time because Israel was then a dominant military power. Yet the scale of the defeat would be extensive -- all that would be left of Israel is likened to a sheep that had been mauled by a wild animal (v. 12).
Why would this happen? Amos mentions the reasons in the next verses. Israel had been guilty of idolatry (v. 14) and luxurious living (v. 15). In particular, he is addressing the ruling classes here and also adds that they were guilty of oppressing the poor (4:1). Their fortresses would not prevent them going into captivity (4:2-3), led in chains by hooks on their noses.
The people of Israel had forgotten their God and instead participated in idolatry. Forgetting God soon led them to forget their relationship to one another. Instead of showing brotherly love they practised the opposite. Those who had plenty trampled on those who had little.
Here is a reminder that ongoing brotherly love depends on an ongoing relationship with God. If our relationship with God cools or ceases, so will our relationship with one another. Instead of a church being a family, it can become the opposite, and when that happens, what future can it have?