A Spiritual Meaning to be Learned

Surely there's a spiritual meaning we can learn from this. My first thought when I saw this was the spread of the gospel and discipleship. If one person acting in obedience makes an impact on at least 2 others (he mentions the number 1.5, but you can't affect half a person so the analogy isn't perfect, I know) then they, in turn, impact roughly 2 other people each, etc., we'll eventually make a loud "boom" for Christ's kingdom.