What was the main signpost which David pointed out to keep his son on the godly path?

(8 mins. reading time)

In my mind I picture the signpost on a hiking trail at a conservation area near our home which has several trails, each with their own coloured-coded signs. If you want to take the green trail, then follow the green signs. If you want to follow the yellow trail, then take the yellow signs. It’s clear that to stay on the trail you need to follow the coloured signs. Following the yellow signs will never put me on the green trail. David began by describing the trail to avoid.