Obedience does not consist in paying God back and thus turning grace into a trade. Obedience comes from trusting in God for more grace - future grace - and thus magnifying the infinite resources of God's love and power.
John PiperThat's who Jesus Christ is. He became the final Priest and the final Sacrifice. Sinless, he did not offer sacrifices for himself. Immortal, he never has to be replaced. Human, he could bear human sins. Therefore he did not offer sacrifices for himself; he offered himself as the final sacrifice. There will never be the need for another. There is one mediator between us and God. One priest. We need no other. Oh, how happy are those who draw near to God through Christ alone.
John Piper