'The first resurrection,' mentioned in Revelation 20:5, 6, does not mean a first resurrection, but the essence and primary part of resurrection, which is salvation and eternal life. There is only one resurrection to life. A second does not happen, and is not mentioned anywhere in the Bible.

(References: Apocalypse Explained 6; Apocalypse Revealed 851; Revelation 20:5-6)

Spiritually, "beginning" happens when we first start new growth -- new levels of awareness and willingness to receive goods and truths from the Lord, and use them. In the Word, "beginning" doesn't just mean the beginning of something in time. In the inner sense, it means the initial phase of a spiritual state.