Meanings of becomes a duty in English

And what happens when the reward becomes a duty, too?

The seclusion prescribed by the East becomes a duty, a moral obligation, a virtue.

The Isle must be small, too, because since it is yours it becomes a duty to exhaustively comprehend it.

It becomes a duty to keep society going, and give it the sort of tone that a nice woman can do.

When opinion reaches this stage, adhesion becomes a duty; and henceforward the few who are capable of forming a judgment hold their peace.

Play becomes a duty, imagination becomes second hand, the goal of the children degenerates into guessing what will please the parents and earn praise.

As Literature everyone has the right to examine the contents critically, and, considering the importance attributed to the contents, the right becomes a duty.

"I feel that it is a case where true altruism becomes a duty."

"Can you always forget when it becomes a duty?"

"Keep close to me, Emily," said Louis, "and I will make the speeches if it becomes a duty."