May the bolts of your gate be iron and bronze, and may your strength match your days.” — Deuteronomy 33:25

As your days, so shall your strength be. God's promise isn't a warehouse of strength for tomorrow—it's daily bread. Don't worry about tomorrow; today's trouble is enough for today. The God of Israel gives strength and power to His people. When Paul is weak, then he's strong because Christ's power rests on him.