For those who have responded to their Lord is the best [reward], (13:18)

Almuntakhab Fi Tafsir Alquran Alkarim

Those who respond favourably to Allah, the Creator, and lift to Him their inward sight are the recipients of Allahs blessings and gratifying rewards, whereas those who do not respond and their hearts dare rise defiant against Him were born to be losers. If they have profuse affluence of all things on earth and twice as much, they would gladly give it in expiation of their guilt at Judgment, but far from it. These and their like must expect a manifest discomfort of body and mind. Much misery and hardship shall be the insignia of their reckoning when the account of their life and conduct is rendered at Judgment. Their abode is Hell and evil indeed is the bed they have made for themselves

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

(13:18) There is an excellent reward for those who responded to the call of their Lord. As for those who rejected His call, they would willingly give for their ransom all the wealth the earth contained, if they possessed it, and as much more besides (in order to escape retribution). *33 Those are the people who shall have the heavy reckoning; *34 their abode shall be Hell-a wretched resting place.

For those who have responded to their Lord is the best [reward], meaning

*33) This shows that the disbelievers would be in such a sad plight that they would not hesitate to give their alI for their redemption.
*34) ".... they shall have the heavy reckoning": they shall have to bear the full consequences of their evil deeds. No sin, no shortcoming, in short, nothing will be forgiven and no evil shall go un-punished.
We learn from the Qur'an that the rebels of AIIah shall have to render a reckoning, whereas there shall be a "light" reckoning from those who have been faithful and obedient to their Lord. In consideration of their loyal services, their cases will be dealt with leniently, and taking their general goodness into account many of their shortcomings will be forgiven.
This is further amplified by a Tradition of the Holy Prophet. Hadrat 'A'ishah relates, "I said, O Messenger of Allah !the most dreadful verse of the Qur'an is this: Whoso shall commit an evil, he shall be punished for it'. (IV :123). The Holy Prophet answered, O `A'ishah! don't you know how Allah clears the accounts of His faithful and obedient servant? Whatever harm or trouble he receives in this world-even so much as the pricking of a thorn-is taken by Allah as atonement for one or the other of his sins. As regards the Hereafter, everyone, who shall be called upon to render an account of any sin, shall be punished for it' . At this Hadrat `A'ishah asked, `Then what is meant by light reckoning in this verse: Whoso shall be given his `Conduct Register' in his right hand, he will render a light reckoning?' (LXXXIV:?-8). The Holy Prophet answered, `This means merely the presentation of his whole conduct, that is, all his deeds-good and bad-shall be presented before Allah but he shall not be called upon to clear the account of all his deeds; for the one who shall be called upon to clear the whole of his account, shall be totally ruined' . "
The same thing is happening even in this world. A master deals very leniently with his faithful and obedient servant and connives at his minor faults and even forgives his major faults in consideration of his meritorious services. On the other hand, if a servant is proved to be treacherous and dishonest, no consideration is given even to his services, and he is punished both for his minor and for major faults.
 

For those who have responded to their Lord is the best [reward], meaning in Urdu

جن لوگوں نے اپنے رب کی دعوت قبول کر لی ہے اُن کے لیے بھلائی ہے اور جنہوں نے اسے قبول نہ کیا وہ اگر زمین کی ساری دولت کے بھی مالک ہوں اور اتنی ہی اور فراہم کر لیں تو وہ خدا کی پکڑ سے بچنے کے لیے اس سب کو فدیہ میں دے ڈالنے پر تیا ر ہو جائیں گے یہ وہ لوگ ہیں جن سے بری طرح حساب لیا جائے گا اور اُن کا ٹھکانہ جہنم ہے، بہت ہی برا ٹھکانا