This is an example of what is called a composition
of the "Sacred Conversation" genre: the insertion of Saints and or
Angels with an idyllic scene of the Holy Family or Madonna and Child.
This was perhaps the most often used artistic device of the period.
Lotto's painting is exhibited regularly at Catholic Tradition,
sometimes in the Angels' annual presentation, and usually in at least
one Madonna gallery, the most recent was in September of 2005. And it
is now part of this permanent gallery.