Make us steadfast, O Lord, by saying it, that is, the testimony lā ilāha illā Allāh. This is a reference to the Quranic verse: Allah makes the believers steadfast with the firm Word in this worldly life and the Hereafter [14:27]. Al-qawl al-thābit (the firm word) is explained in the standard tafsīrs as being: lā ilāha illā Allāh.

     And benefit us, O Guardian Lord, by its mention and remembrance. This also refers to the shahāda lā ilāha illā Allāh. Sīdī Ibn ʿAjība says in his commentary on the Waẓīfat al-Zarūqiyya, “Its benefit in this life is that it safeguards from Satan and his forces, protects life and property, and makes firm our steps in places of tribulation and fright, and its benefit in the hereafter at the moment of the questioning and meeting with Allah is the most excellent reward and Divine Grace.”      

     And bring us inside the domain of its citadel.  In a ḥadīth qudsī:  "Lā ilāha illā Allāh is My citadel, and whoever enters My citadel is safe from My punishment." This is quoted in Abū Nuʿaym, Ḥilyat al-awliyāʾ  and in the commentary of imam al-Rāzī

     And make us among its people, and at the moment of death, one of those who pronounce it and know it. Muʿādh ibn Jabal said, “The Messenger of Allah said, ‘He whose last word is lā ilāha illā Allāh enters Paradise.” Al-Nasā’ī in his Sunan, Aḥmad b. Ḥanbal, Musnad, Abū Dāwūd, Sunan, al-Bayhaqī, Shuʿab al-īmān, Ibn Ḥibbān, Ṣaḥīḥ.

     And resurrect us among the ranks of our master and guardian, Muḥammad, may Allah bless him. The word zumratu (translated above as “ranks”) means “a  group” or “throng of people” and in its plural is the name of the Sūra 39 (al-Zumar), where it is mentioned in verses 71 to 73 describing the unfaithful being driven into hell in throngs (zumara) and the Godfearing being driven into paradise in throngs. 

     And in a ḥadīth in Bukhārī and Muslim, the Messenger of Allah is reported by Abū Hurayra (R) to have said, “There will be seventy thousand from my community who enter paradise as a single group (zumratan) their faces as bright as the full moon.”