dhanb, a sin whose outcome is detestable.

āmanū: they believed with their hearts, professed with their tongues, and acted with their limbs—the pinnacle of all that is tawḥīd (pure monotheism).

yalbisū īmānahum: they do not mix their monotheism.

bi-ẓulmin: with wrongdoing, here meaning shirk (polytheism). Wrongdoing is to place something where it does not belong; shirk is called ẓulm because it directs worship to one who does not deserve it.

al-amn: inner tranquillity and the removal of fear.

muhtadūn: those granted success to walk the straight path and to remain firm upon it.

Overall meaning of the verse: The Almighty tells us that those who devote worship solely to Allah and do not taint their monotheism with polytheism will be secure from terrors and hardships on the Day of Resurrection and will be guided to tread the straight path in this life.

Relevance of the verse to the chapter: It shows the excellence of tawḥīd and its ability to expiate sins.

Lessons derived from the verse:
1- The merit of tawḥīd and its fruits in this world and the Hereafter.
2- Shirk is wrongdoing that nullifies faith in Allah if major, and diminishes it if minor.
3- Shirk is never forgiven.
4- Shirk brings about fear in both this world and the next.