Before Christ came, priests represented the people in matters related to God. Priesthood was a gift (from Hebrews 5:1, Numbers 18:7).
Now we have a great high priest, Jesus, the Son of God. He sympathizes with weakness, understands temptation, and offers mercy and grace (from Hebrews 4:14-16).
We pray with confidence because Jesus represents us.
A Blog on Prayer 