Surah 57. Al-Hadid, Ayah 19

I.e., by their readiness for any sacrifice.

Cf. iv. 69, and n. 586. The four categories there mentioned as constituting the beautiful Company of Faith are: the Prophets who teach, the Sincere Lovers of Truth, the Martyrs, and the Righteous who do good. Of these, the prophets or messengers have already been mentioned in this verse. The Righteous who do good are mentioned as the men and women given over to deeds of charity in verse 18.

The Martyrs (witnesses) are all those who carry the Banner of Truth against all odds and in all positions of danger, whether by pen or speech, or deed or counsel.

Note that these two are specially high degrees in the Hereafter, just short of Prophethood. For they have not only their reward in the Hereafter, like those who practise charity (verse 18 above), but they themselves become sources of light and leading.