He means that the believers in Allah and His messengers are with Allah in the status of the truthful and the martyrs. They are those who preceded in believing and were martyred in the way of Allah. For them is their reward and their light, meaning: like the reward of the truthful and the martyrs and like their light. If you say: How can they be equated in reward when there must be a difference? I say: The meaning is that Allah gives the believers their reward and multiplies it for them by His grace, until their reward equals the multiplied reward of those. It is also possible that 'and the martyrs' is a subject, and 'for them is their reward' is its good.