There will never be doctrinal unity, even within Catholicism. The quest for such unity on an ecumenical level is an even more obvious theological will-o-the-wisp.

The ground of unity is love; nothing less. And absolutely nothing more. 

Love's signature is not just respect for diversity (even if it is doctrinal), but actually welcoming it as attempts to parse the mystery of divine truth.

Unfortunately, both Pope Francis and Archbishop Welby consider their differences as "serious obstacles" and not as opportunities for tolerance, acceptance, and ecumenical integration.