Ma'arif al-Qur'an
Mufti Muhammad ShafiA self-opinionated deed and an act of religious innovation, no matter how appealing, is not acceptable
In this verse (19), by adding the word: سَعْيَهَا (as due), it has been made explicit that every deed and every effort is not necessarily beneficial or acceptable with Allah. Instead, the only deed or effort credible is that which is appropriate to the essential objective (of the Hereafter). And whether or not it is appropriate can only be found out from the statement of Allah Ta’ ala and His Messenger ﷺ . Therefore, even well meaning efforts made by insisting on bland personal opinion and self-invented ways - which includes common customs of Bid'ah (innovations in established religion) - no matter how good and beneficial they may appear at their face, but are not appropriate to the effort made for the Hereafter. Consequently, they are neither acceptable with Allah nor are they of any use in the Hereafter.
Explaining the word: سَعْيَهَا (as due), Tafsir Ruh al-Ma’ ani says that the 'effort' should be in accordance with 'sunnah.' Along with it, it adds that this effort or deed should also have uprightness and firmness. In other words, this deed should be beneficial in accordance with the Sunnah as well as it should be upright and constant. Doing it haphazardly or doing it in a cycle of doing and not doing is not good. It never yields the maximum benefit.