وَأَنَّ سَعْيَهُ سَوْفَ يُرَ‌ىٰ (and that his effort will soon be seen...53:40) In other words, outer actions of a person are not sufficient. Allah will take into account the real, inner motive and driving force behind them whether they were performed with the sincerity of purpose, or they were done with some ulterior motive. The Holy Prophet t is reported to have said:

اِنَّمَا الاَعمَال بِالنِّیَّاتِ

"Actions shall be judged only by the intentions."

That is, the outer aspect of actions is not sufficient. The inner aspect is also necessary. Actions must be performed purely for the good pleasure of Allah and in compliance with His command.