The Quran

وَلا تَطرُدِ الَّذينَ يَدعونَ رَبَّهُم بِالغَداةِ وَالعَشِيِّ يُريدونَ وَجهَهُ ۖ ما عَلَيكَ مِن حِسابِهِم مِن شَيءٍ وَما مِن حِسابِكَ عَلَيهِم مِن شَيءٍ فَتَطرُدَهُم فَتَكونَ مِنَ الظّالِمينَ

Muhammad Asad

Hence, repulse not [any of] those who at morn and evening invoke their Sustainer, seeking His countenance.¹ Thou art in no wise accountable for them - just as they are in no wise accountable for thee² - and thou hast therefore no right to repulse them: for then thou wouldst be among the evildoers.³

According to Traditions, this and the next verse were revealed when, several years before the Muslims' exodus to Medina, some of the pagan chieftains at Mecca expressed their willingness to consider accepting Islam on the condition that the Prophet would dissociate himself from the former slaves and other "lowly" persons among his followers - a demand which the Prophet, of course, rejected. This historical reference does not, however, provide a full explanation of the above 'passage. In accordance with the Qur'anic method, allusions to historical events - whether relating to contemporary occurrences or to earlier times - are always made with a view to expressing ethical teachings of a permanent nature; and the passage under consideration is no exception in this respect. As the wording shows, it relates not to "lowly" followers of Islam but to people who, while not being Muslims in the current sense of this word, believe in God and are always ("at morn and evening") "seeking His countenance" (i.e., His grace and acceptance): and, thus, verses 52-53 connect logically with verse 51. Although primarily addressed to the Prophet, the exhortation voiced in this passage is directed to all followers of the Qur'an: they are enjoined not to repulse anyone who believes in God - even though his beliefs may not fully answer to the demands of the Qur'an - but, on the contrary, to try to help him by means of a patient explanation of the Qur'anic teachings.
I.e., for whatever in their beliefs or actions does not coincide with the teachings of the Qur'an, and vice-versa. In, other words, all are accountable to God alone.
Lit., "so that thou shouldst repulse them and thus be of the evildoers".