1. The first and last; signifies God's eternity.
2. The basic meaning of something; the crucial part; the most important aspect of something.

The beginning and the end, the first and the last, as in "She had to master the alpha and omega of the new computer program before she could even begin."

This idiom and its meaning, based on the first and last letters of the Greek alphabet, appears in the New Testament (Revelation 1:8): "I am Alpha and Omega, the beginning and the ending, saith the Lord," where it is repeated three more times.