The image of rotting roots reflects human transience (the short and fragile nature of human life; see Isaiah 11:1; 27:6; 37:31).
To despise the Lord’s word means to reject or ignore it. It means living without concern for obeying what God has said.
This attitude leads to folly (foolish living) and ruin (Proverbs 1:30; 5:12; 15:5).