When we look at the biblical phrase "coh amar y'adonai" - "thus says the Lord" - it is common to think that it either introduces God's promise or judgment on his people. But sometimes it introduces both in the same verse. Amos 5:3 says, "For thus says the Lord GOD: 'The city that goes out by a thousand shall have a hundred left, and that which goes out by a hundred shall have ten left to the house of Israel'" (NKJV).
There are three kinds of images being used here: warfare language, tithing ideas, and remnant concepts. What God is describing is Israel going to war. In the ancient world, cities would send out their armies to fight other armies on the plain, whether in front of their own city or in front of their enemy's city. The armies of cities would usually retreat back inside their city walls if a number of their soldiers were killed. If only twenty or thirty percent of your army remained from the fighting, this was generally considered a catastrophic loss (not only of the battle, but of the fighting force). And this is what God is telling Israel: if it sends one thousand solders to battle, only one hundred (ten percent) will return; if it sends one hundred soldiers to battle, only ten (ten percent) will return.
The suggestion in Amos 5:3 is not that Israel isn't strong enough to wage war or defend itself, but that God is giving Israel a wakeup call about its refusal to be in relationship with God (cf. Amos 4). Nevertheless, God leaves Israel with hope. Even though God will show Israel how weak it is by only giving a tithe of its military forces back to the nation, this ten percent is also a remnant. Most of Israel's army will be destroyed, but God will preserve a remnant of that force - not because Israel is strong, but because God is good and kind.
Friends, it can be easy to think that we are in control of the details of our lives, and that we either only need a little of God's help or we don't need God's help at all. But the truth is that we are preserved only because God is loving and, in that love, God speaks redemption and salvation into our lives. Let us trust in God rather than our own ability to get ourselves out of trouble, because "thus says the Lord."