Tehillim 119:21
גערת זדים ארורים השגים ממצותיך
ga'arta zedim arurim hashogim mimitzvoteicha
You have rebuked the accursed insolent ones who stray (err) from Your commandments.
The fifth obstruction is the antagonism of the nations. They believe that they adhere to the commandments of the Torah, when actually they err and distort, and so are perpectually cursed. That is what it says here, "You have rebuked the accursed insolent ones who err from Your commandments."
Some explain the verse as referring to the future rather than the past. You will curse "the accursed insolent ones who err from Your commandments." They willfully distort what they study of the Torah, and so err at keeping the mitzvot.
The "insolent ones... err." Their insolence causes them to err.
Some say: They "err away from Your commandments." There are "accursed insolent ones" who expound the Torah superficially, contrary to Halachah. That is, they bring halachically-invalid proofs for their false doctrines. For this reason were the Tablets of the Law written front and back, to convey that if one comes to be purified (to be the same inside and out), he is helped. But if one comes to be defiled - he wants to "stray from Your commandments" - he is abandoned ot his choice.
- Me'am Lo'ez
Tehillim 119:21
