Soldiers in the field of battle risk personal danger and death to help a fellow soldier. They are so focused on getting their buddy to safety that they disregard personal danger to themselves.

So these words of Jesus might be rephrased in this manner:

'If any would be my disciple, let them become so wrapped up in doing the will of God, so taken up with concern for others, they forget about themselves.

'For the ones who live only for themselves will actually miss life altogether, and those who lose their lives in their concern for others, in doing God's will, will find fulfillment and satisfaction in life, which is authentic life.'