﴿ إِنَّمَا ٱلْمُؤْمِنُونَ ٱلَّذِينَ ءَامَنُوا۟ بِٱللَّهِ وَرَسُولِهِۦ ثُمَّ لَمْ يَرْتَابُوا۟ وَجَٰهَدُوا۟ بِأَمْوَٰلِهِمْ وَأَنفُسِهِمْ فِى سَبِيلِ ٱللَّهِ ۚ أُو۟لَٰٓئِكَ هُمُ ٱلصَّٰدِقُونَ ﴾

“[Know that true] believers are only those who have attained to faith in God and His Apostle and have left all doubt behind, and who strive hard in God’s cause with their possessions and their lives: it is they, they who are true to their word!”

The true believers that is those who are true in their affirmation of faith — as He makes explicit in what follows — are only those who believe in God and His Messenger and then have not doubted they have not been uncertain of their faith and who strive with their wealth and their souls for the cause of God hence their striving manifests the sincerity of their faith. It is they who are sincere in their faith not those who say ‘We believe’ and from whom all that has been forthcoming is their submission to the religion.