When God makes a covenant, he makes the greater promises. His people promise to love him and to obey him. But God promises to change their lives completely. He forgives their evil deeds. He makes them free. He even adopts them as his sons and daughters! (See Galatians 4:4-7 and 1 Peter 2:4-10).
The mediator is the person who arranges the covenant. And Jesus is the mediator of the covenant between God and his people. When he lived on earth, he spoke to us on behalf of God the Father (John 12:49-50). And now, in heaven, he speaks to God the Father on our behalf (Hebrews 7:25).
So Jesus is the chief priest of the new covenant between God and his people.
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