Khayrkhwah, Khwāja Muḥammad Riḍā b. Sulṭān Ḥusayn, writes in his 16th century epistle “The Epistle” (Risāla) that the purpose of this life is to recognize God with conviction ("taḥqīq") and certainty ("yaqīn"). According to “The Epistle”, the Ismaili spiritual hierarchy ("ḥudūd-i dīn") consists of the proof ("ḥujjat") who holds the highest rank, followed by the "dāʿīs," "muʿallims", greater "maʾdhūns", and lesser "maʾdhūns". Khwāja Muḥammad points out that the proof ("ḥujjat") belongs to the first category of people who testified to the sovereignty of God with conviction ("taḥqīq"). There is a second category who also testified, but only in imitation of the first, rather than with conviction ("taḥqīq"). The purpose of the first category of people is to nurture the souls of those of the second category. He also points out that although the proof ("ḥujjat") belongs to the first category, the other members of the hierarchy belong to the second category.