Liyuwaffiyahum ojoorahum wayazeedahum min fadlihi innahu ghafoorun shakoor (surah Fatir: 30)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(35:30) (a trade in which they have invested their all) so that Allah may pay them their wages in full and may add to them out of His Bounty. *51 He is Most Forgiving, Most Appreciative. *52

Liyuwaffiyahum ujoorahum wa yazeedahum min fadlih; innahoo Ghafoorun Shakoor

*51) This kind of conduct and practice of the believers has been likened to a trade bargain because in trade a man invests his money and labour and capabilities in the hope that he will not only get his capital back and his wages for the time and energy spent but in addition some profit as well. Likewise, a believer also invests his wealth and his time and his labour and capabilities in carrying out Allah's Commands and in His service and worship and in the struggle to promote the cause of His Religion in the hope that he will not only get his full rewards for it but Allah will bless him with much more from His bounty as well. But there is a great difference between the two kinds of bargains. In the worldly trade bargains there is the risk of loss also along with the hope of profits. Contrary to this, in the bargain that a sincere servant makes with his God there is : no risk of any loss whatever.
*52) That is, "Allah's relation with the sincere believers is not that of a miserly master who checks his servant on trivialities and brings all his services and loyalties to nought on account of a minor error. But Allah is the Most Beneficent. and Generous Master. He overlooks the errors of His obedient servant and appreciates whatever service he might be able to render. "