"Except the seeking," meaning: he does not do that except to seek "the Countenance of his Lord, the Most High, and he shall surely be content," with the reward in Paradise. It is said that it was revealed regarding Abu Bakr al-Siddiq when he emancipated Bilal and six others with him.
﴿إِلَّا ابْتِغَاء﴾ أَيْ: لَيْسَ يَفْعَلُ ذَلِكَ إِلَّا ابْتِغَاءَ ﴿وَجْهِ رَبِّهِ الأَعْلَى وَلَسَوْفَ يرضى﴾ الثَّوَابَ فِي الْجَنَّةِ، وَيُقَالُ: إِنَّهَا نَزَلَتْ فِي أَبِي بَكْرٍ الصِّدِّيقِ حِينَ أَعْتَقَ بِلالًا وَسِتَّةً مَعَهُ.