Jesus is a far better priest than any human priest, even better than Melchizedek. Jesus has blessed us, like Melchizedek blessed Abraham. As such we should give our lives to Jesus as Abraham gave a tithe to Melchizedek.
We can hold on to Jesus because God, who cannot lie, has promised that our High Priest, Jesus, is a sure and steady anchor already ministering on our behalf before God.
Furthering the imperative, the author of Hebrews invites us to strive to enter the rest of God by continuing to believe in the Gospel and drawing near to Christ in our time of need (temptation).