The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
33. But (Brahman's creative activity) is mere sport, such as we see in ordinary life.
The word 'but' discards the objection raised.--We see in every-day life that certain doings of princes or other men of high position who have no unfulfilled desires left have no
reference to any extraneous purpose; but proceed from mere sportfulness, as, for instance, their recreations in places of amusement. We further see that the process of inhalation and exhalation is going on without reference to any extraneous purpose, merely following the law of its own nature. Analogously, the activity of the Lord also may be supposed to be mere sport, proceeding from his own nature 1, without reference to any purpose. For on the ground neither of reason nor of Scripture can we construe any other purpose of the Lord. Nor can his nature be questioned 2--Although the creation of this world appears to us a weighty and difficult undertaking, it is mere play to the Lord, whose power is unlimited. And if in ordinary life we might possibly, by close scrutiny, detect some subtle motive, even for sportful action, we cannot do so with regard to the actions of the Lord, all whose wishes are fulfilled, as Scripture says.--Nor can it be said that he either does not act or acts like a senseless person; for Scripture affirms the fact of the creation on the one hand, and the Lord's omniscience on the other hand. And, finally, we must remember that the scriptural doctrine of creation does not refer to the highest reality; it refers to the apparent world only, which is characterised by name and form, the figments of Nescience, and it, moreover, aims at intimating that Brahman is the Self of everything.
457:1 The nature (svabhâva) of the Lord is, the commentators say, Mâyâ joined with time and karman.
457:2 This clause is an answer to the objection that the Lord might remain at rest instead of creating a world useless to himself and the cause of pain to others. For in consequence of his conjunction with Mâyâ the creation is unavoidable. Go. Ân. Avidyâ naturally tends towards effects, without any purpose. Bhâ.
Ân. Gi. remarks: Nanu lîlâdâv asmadâdînâm akasmâd eva nivritter api darsanâd îsvarasyâpi mâyâmayyâm lîlâyâm tathâbhâve vinâpi samyaggñânam samsârasamukkhittir iti tatrâha na keti. Anirvâkyâ khalv avidyâ parasyesvarasya ka svabhâvo lîleti kokyate tatra na prâtîtikasvabhâvâyâm anupapattir avataratîty arthah.