That the Father dwells in the Son, shews that He is not single, or solitary; that the Father works by the Son, shews that He is not different or alien. As He is not solitary who doth not speak from Himself, so neither is He alien and separable who speaketh by Him. Having shewn then that the Father spoke and worked in Him, He formally states this union: Believe Me that I am in the Father, and the Father in Me: that they might not think that the Father worketh and speaketh in the Son as by a mere agent or instrument, not by the unity of nature implied in His Divine birth.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: vii. de Trin