64. say: o' people of the book! come to a ward common between us and
you, that we worship none but allah,
and that we associate not anything with him,
and (that) some of us do not take any others for
lords other than allah `
and if they turn back, then say:
'bear witness that we are muslims'."

commentary:
an invitation to unification

in the former verses, the direction of invitation was towards islam
with its all specialities but, in this verse, the aim is an invitation to the
common points between islam and other creeds of the people of the
book it addresses the prophet (p.b.u.h.) and states:

" say: 'o' people of the book! come to a ward common between us and
you, that we worship none but allah, and that we associate
not anything with him, and (that) some of us do not take any others for
lords other than allah'. ..."

by this method of reasoning, it teaches us that if there are some
people who are not willing to cooperate with us in all holy aspects, we
may try to attract their cooperation at least in common aims and utilize
it as a base for the progression of our holy affairs
then, at the end of the verse, it say:

"... and if they torn back, then say: 'bear witness that we are muslims'."

that is, after this logical invitation to the common points of
theism, when they still reject the truth, tell them:

we totally submit to allah but you do not. and, therefore, your
distance from the truth will not have the least effect on our selves and
we will keep and continue our way, viz. the path of islam. so, we
worship allah alone, and only his laws we follow. and, there will be
no human worshipping, of any kind, among us.