Isaiah notes that the people of God are trusting in rituals to save them, when God looks for repentance in their hearts. In Luke we have seemingly contradictory advice: don’t worry about the future, but be prepared. A closer reading says don’t worry about the physical needs, but be prepared on the spiritual level for Christ to return. Both passages remind us that God is looking a heart turned toward the Lord.
If we keep our hearts open to God, God will make sure everything else will fall in place.