Only those are Believers who have believed in Allah and His Messenger, and have never since doubted, but have striven with their belongings and their persons in the Cause of Allah: Such are the sincere ones.
After v. 14 rebuked those who claim belief without attaining it, this
verse emphasizes the steadfast nature of true faith and the depth of commitment
it entails. While the previous verse emphasizes obedience, this verse emphasizes
belief. Those who strive with their wealth and theirselves in the way of God (cf.
8:72; 9:20, 44, 81; see also 2:218; 4:95; 5:35, 54; 8:74; 9:41) are those who are
willing to give everything for the sake of seeking God’s good pleasure (IK); see
4:95c; 8:72c. They are truthful in their claim to believe, unlike the members of
the Banū Asad, who claim belief only outwardly (IK).
Nasr, Hossein (2015). Study Quran. http://www.islamicweblibrary.com/wp-content/uploads/2020/04/TheStudyQuran.pdf