When someone gives you a gift, you simply receive it and thank the person who gave it. You don't try to pay for it. You don't try to reciprocate by giving the person a gift also so that you won't have any obligation. Such an attitude will be an insult to the giver unless the gift was not really a gift but a form of manipulation. Righteousness is a gift from God. It is freely given with no strings attached. We are simply to receive it by faith with thanksgiving in our hearts.