What it is
Alpha (Α) is the first letter of the Greek alphabet and omega (Ω) is the last. Paired together, they stand for "from beginning to end" — a typographic equivalent of "from A to Z" in English.
Where it comes from
The pair takes on theological weight from the book of Revelation, where Christ declares Himself the Alpha and the Omega — the Beginning and the End. The phrase appears three times: at the book's opening (Revelation 1:8↗), at the throne vision of the new creation (Revelation 21:6↗), and at the book's close (Revelation 22:13↗). In each, the title belongs to God or to Christ; the two are bound together in the same self-revelation.
Where you'll see it
Christian art has paired alpha and omega with the chi-rho since late antiquity — the two often appear together flanking the chi-rho mark in mosaic, manuscript, and architectural settings. The pair appears independently on church facades, in stained glass, on bishops' staves and pectoral crosses, and in the liturgical traditions' calendars and vestments.
Why it's the SumBible section-divider symbol
Every section of a scriptural reflection — every chapter, every book — sits inside the larger arc that begins with creation and ends with the consummation Christ Himself names in Revelation. Alpha and omega between two horizontal lines is a quiet way of marking that arc at every visual break on the page: a reminder that whatever this section is about, it sits between two ends Christ Himself has named.