[Pooya/Ali Commentary 23:8] This verse refers to the whole canvas of obligations a Muslim undertakes to fulfill. Verse 177 of al Baqarah also says that a true believer is he who fulfills his promises and abides by the covenant he makes. In 10 Hijra, at Ghadir Khum, all those who were present there made a covenant with Allah and his prophet that they would obey Imam Ali, after the Holy Prophet, in his place, as their wali and mawla (see commentary of al Ma-idah: 67), but history shows us that they did not fulfill their covenant, so they are out of the group of believers mentioned in verses 1 to 11 of this surah.