"For this reason he had to be made like his brothers in every way, in order that he might become a merciful and faithful high priest in service to God, and that he might make atonement for the sins of the people." NIV translation
The high priest was a man that was the mediator between God and his fellow man. By being fully God and fully man, Jesus bridged that gap permanently with His sacrifice.
"Because he himself suffered when he was tempted, he is able to help those who are being tempted." NIV translation
Jesus was tempted by the devil (see Luke 4) and did not sin. He became the perfect payment for our sins and overcame Satan by His resurrection. Therefore, He is able to save us from our sins. He also sent the Holy Spirit to live in us and to help us to overcome the temptations of the devil.