The Quran

قالوا سُبحانَكَ ما كانَ يَنبَغي لَنا أَن نَتَّخِذَ مِن دونِكَ مِن أَولِياءَ وَلٰكِن مَتَّعتَهُم وَآباءَهُم حَتّىٰ نَسُوا الذِّكرَ وَكانوا قَومًا بورًا

Muhammad Asad

They will answer: "Limitless art Thou in Thy glory! It was inconceivable for us to take for our masters anyone but Thyself!¹ But [as for them - ] Thou didst allow them and their forefathers to enjoy [the pleasures of] life to such an extent that² they forgot all remembrance [of Thee]: for they were people devoid of all good."

Sc., "and so it would have been morally impossible for us to ask others to worship us". On the other hand, Ibn Kathir understands the expression "for us" (lana) as denoting "us human beings" in general, and not merely the speakers - in which case the sentence could be rendered thus: "It is not right for us [human beings] to take...', etc. In either case, the above allegorical "question~and~answer" - repeated in many variations throughout the Qur'an - is meant to stress, in a dramatic manner, the moral odiousness and intellectual futility of attributing divine qualities to any being other than God.
This is the meaning of harta (lit., "till" or "until") in the present context.