Conversation so far:
What was Basel in relation to Hans Holbein the Younger?
Basel was where Hans Holbein the Younger worked as a young artist and where he bought a house in St Johanns-Vorstadt.
What did Hans Holbein the Younger use the Basel house for?
Hans Holbein presumably returned home to preserve his citizenship, since he had been granted only a two-year leave of absence to England.
What was significant about Hans Holbein the Younger's house in Basel?
What other things happened during this period in Basel for Hans Holbein the Younger?
Basel's reformist iconoclasts probably destroyed some of Hans Holbein's religious artwork, but details are unknown.

Question: What was significant about that painting?
Self-contained rewrite: What was significant about that Hans Holbein the Younger's The Artist's Family painting?