I judge that the correct reading in the Greek is without the article. This construction directs the mind to all the component parts of the thing in question. So here the building is not viewed as one completed thing but was 'growing to' a temple (naos). He is looking at a building composed of living stones as a whole, but mentally apprehended as composed of many parts. Among these, in Christ, the Gentiles at Ephesus were built in too, to be now already a habitation of God by the presence of the Spirit.