In these chapters the persistent theme is that of God testing Israel’s faithfulness to Him by the pagan nations that surrounded them:
7 The sons of Israel did what was evil in the sight of the Lord, and forgot the Lord their God and served the Baals and the Asheroth. 8 Then the anger of the Lord was kindled against Israel, so that He sold them into the hands of Cushan-rishathaim king of Mesopotamia; and the sons of Israel served Cushan-rishathaim eight years. 9 When the sons of Israel cried to the Lord, the Lord raised up a deliverer for the sons of Israel to deliver them, Othniel the son of Kenaz, Caleb’s younger brother. 10 The Spirit of the Lord came upon him, and he judged Israel. When he went out to war, the Lord gave Cushan-rishathaim king of Mesopotamia into his hand, so that he prevailed over Cushan-rishathaim. 11 Then the land had rest forty years. And Othniel the son of Kenaz died. (3:7-11)
This pattern repeats itself over and again. First, Israel is indicted for worshipping demons, not the one true God (3:12; 4:1-2) and God sells them into the enemy’s hands:
“Now the sons of Israel again did evil in the sight of the Lord. So the Lord strengthened Eglon the king of Moab against Israel, because they had done evil in the sight of the Lord.” (3:12)
“Then the sons of Israel again did evil in the sight of the Lord, after Ehud died. 2 And the Lord sold them into the hand of Jabin king of Canaan, who reigned in Hazor; and the commander of his army was Sisera, who lived in Harosheth-hagoyim.” (4:1-2)
If we don’t worship the Deliverer, He will deliver us into the hands of our tormentors. This is exactly what Paul argues for in (Rom.1:18-32) where God gives over those who exchanged His glory for the creatures: He gave them over in the lusts of their hearts (1:24), gave them over to degrading passions (1:26), and gave them over to a depraved mind (1:28). The heart, passions and mind were all affected. It happened then, it happens now.
Second, when God’s covenant people cry out for rescue, He hears their sobs and acts through sending Othniel, Ehud, and Deborah in order to save them (3:9, 15; 4:4).
Third, their slavery to these foreign “gods” and nations is never more than the rest they receive in the land by God’s hand (3:8 eight years of bondage, forty years of rest 3:11), eighteen years of servitude (3:14) followed by eighty years of rest (3:30), twenty years of bondage (4:3) followed by forty years of peace (5:31). When one generation’s sin plunders them into bondage because of idolatry, the LORD’s rest given to the people is far greater than the time of servitude.
I think this shows us that where sin abounds, God’s grace does much more abound toward vessels of mercy. God’s mercy endures forever, his wrath is but for a moment.