“Horror has taken hold of me because of the wicked that forsake your law.”
When someone who belongs to God turns away from the truth God has given him, it is, as David said, a horrible thing. The definition of “horror” is “an overwhelming and painful feeling caused by something frightfully shocking, terrifying, or revolting.” This is how David felt whenever he saw an Israelite walk away from God’s law.
The truth that God gives us in Christ is infinitely holier than the law God gave to Israel. And for a child of God in this covenant to forsake the truth God gives him is infinitely worse than an Israelite forsaking the law. It is an unspeakable evil. Every time I see it happen, “horror takes hold of me”.