The phrases "my firstborn, my might" and "the beginning of my strength" mean the same thing. The words "might" and "strength" stand for Jacob's ability to produce children. The words "firstborn" and "beginning" mean that [Reuben](rc://en/tw/dict/bible/names/reuben) is his first child. AT: "my first child after I became a man" (See: [[rc://en/ta/man/translate/figs-parallelism]])