The New Testament letter containing the passage about Jesus as the great high priest who passed through the heavens is the Letter to the Hebrews.
Hebrews 4:14 calls believers to hold firmly to their confession because they have a great high priest who has passed through the heavens: Jesus, the Son of God. The passage continues by emphasizing that Jesus can sympathize with human weakness because he was tested in every way, yet without sin.
This priestly theme is central to Hebrews. The letter compares Jesus with the high priests of Israel and presents his priesthood as superior and enduring. It also connects Jesus with Melchizedek, a mysterious priest-king mentioned in Genesis and Psalm 110.
Hebrews is traditionally associated with Paul in some Christian traditions, but the letter itself does not name its author. Modern scholarship generally treats its authorship as uncertain. The title “Hebrews” is traditional and does not mean the work explicitly identifies a Jewish readership.