The first pass I took, I set my eye on a post or something almost all the way across the lawn. Something so far away, I could hardley see it. After I took that pass, I noticed it was very straight. On subsequent passes, I noticed if I didn't continue to keep my eye focused on something far away, that the mowing line would swerve. Even if I looked down only for a moment, even if I focused on following the prior line precisely.
Life is like mowing.
If our eyes are down or on us, our mowing line is going to be crooked. God wants to be our focus. Satan does not want God to be our focus. In fact he may allow anything else to be our focus - hobbies, work, family and even church. These are all good - but God needs to be our focus.