Bhava is often translated as becoming, existence.
It is the support for birth. If there is no existence there is no birth, but that is not quite what it is here about. So there are three becomings, which we are familiar with:
Lust is a passional attitude. When not open to lust there yet can be passion for form (as agreeable, gracious, etc.). And with the 'without form' there are even higher principles to attend to. Becoming with higher principles is esteemed higher and one might end up in higher places, and if we let ourselves in with lower principles we set things up to go to lower places.
Becoming by lust doesn't mean that there is then no form, so it involves more of an orientation, direction, grow: If we don't have passion for the same things, we then don't long for the same things, we then don't take the same things on board, we are then not becoming ("growing", "orienting") along the same things, and so we might not end up at same places.
But, thus so:
'With support of taking up, becoming. With support of becoming, birth'.
Pāḷi-English
Bhava becoming.