The believers are only the ones who have believed in Allāh and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allāh. It is those who are the truthful.
The believers are only those who have faith in Allah and His Messenger, and then do not pollute their faith with doubts and strive in the way of Allah with their wealth and souls, not holding back on anything. Those are the ones truthful in their faith.