You cannot judge another person’s intentions from their clothes, home, or income. Yet the significance of the heart does not excuse harmful conduct accompanied by claims of good intentions. The pairing of قُلُوبِكُمْ and أَعْمَالِكُمْ keeps motives and deeds together.
Consider a person who publicizes a large donation and another who quietly pays a debt owed to someone. The public size of an action does not reveal its sincerity; lawful and upright behaviour also matters.
وَلَكِنْ redirects the statement after the negation. It does not declare neatness, lawful earnings, or proper outward behaviour worthless.