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.

406. Internal Meaning of Genesis, Chapter 5

1-32 Divisions and changes in that church are described, being meant by the posterity of Adam from Sheth.