Ibn Majah

Commentary:

➊
To remain steadfast on the straight path means to remain firm upon the religion of Islam, just as Ibrahim and Ya‘qub (alayhim as-salam) advised their respective children, saying:
﴿فَلَا تَمُوتُنَّ إِلَّا وَأَنتُم مُّسْلِمُونَ﴾ (al-Baqarah: 132/2)
“When death comes to you, let it come to you while you are Muslims.”
The second meaning is to remain upon the path of moderation, avoiding both excess and negligence.
Do not be heedless of remembrance and worship, nor burden yourself so much that it becomes difficult to remain steadfast upon it.

➋
The meaning of (لَنْ تُحْصُوا) is that no person can remain upon the path of righteousness in such a way that no mistake or shortcoming ever occurs from him, nor is it possible to fulfill the due right of remembrance, gratitude, and worship.
This is an allusion to the statement of Allah Ta‘ala:
(عَلِمَ اَن لَّنْ تُحْصُوْه) (al-Muzzammil: 73/2)
“He knows that you will not be able to keep count of it.”
The Messenger of Allah (sallallahu alayhi wa sallam) used to say:
(لَا اُحْصِي ثَنَاءً عَلَيْكَ أَنْتَ كَمَا أثْنَيْتَ عَلٰي نَفْسِكَ) (Sahih Muslim, Kitab al-Salat, Chapter: What is said in bowing and prostration? Hadith: 486)
“O Allah, I cannot fully praise You; You are as You have praised Yourself.”

➌
The continuity or invalidation of ablution (wudu) is something that is generally not known to others, and this matter can easily be kept hidden.
Its observance can only be maintained on the basis of the certainty that whether others know or not, Allah Ta‘ala knows everything.
Preserving ablution means, firstly, to wash the limbs thoroughly in both winter and summer.
Secondly, to wash the limbs attentively during ablution so that no part remains dry.
And thirdly, to remain in a state of ablution as much as possible; and this cannot be accomplished without the strength of faith.

➍
Faith (iman) is an inner state of the heart, the manifestation of which is through actions.
Among actions, the most important is prayer (salah).
Obligatory prayer is such an important act that it has been made a distinguishing sign between disbelief and faith.
The most important attribute of the God-fearing (muttaqin) and the foremost condition for ultimate success and salvation in the Hereafter is prayer.
(See Surah al-Baqarah: 2/5, 2)
Supererogatory (nafl) prayer has its own significance.
When Rabi‘ah ibn Ka‘b al-Aslami (radi Allahu anhu) expressed to the Prophet (sallallahu alayhi wa sallam) his desire for companionship with him in Paradise, the Messenger of Allah (sallallahu alayhi wa sallam) explained the way to attain this station and said:
(فَأَعِنِّيْ عَلٰي نَفْسِكَ بِكَثْرَةِ السُّجُوْدِ) (Sahih Muslim, Kitab al-Salat, Chapter: The virtue of prostration and encouragement towards it, Hadith: 489)
“Help me against your own self by making abundant prostration.”