Names Of The Son

Emmanuel ex Hebraeo in Latinum significat nobiscum Deus, scilicet quia per Virginem natus Deus hominibus in carne apparuit, ut terrenis viam salutis ad coelum aperiret. Ad divinitatis substantiam quae pertinent ista sunt, Deus, Dominus. Deus autem dictus, propter unicam cum patre substantiam. Dominus, propter servientem creaturem. Deus autem et homo, quia verbum et caro. Unde, et bis genitus, dicitur, sive quia Pater eum genuit sine Matre in aeternitate, sive quia Mater sine Patre in tempore. Unigenitus autem vocatur secundum divinitatis excellentiam, quia sine fratribus; Primogentis secundum susceptionem hominis, in qua per adoptionem gratiae fratres habere dignatus est, quibus esset primogenitus. Homousios Patri ab unitate substantiae appellatur. Substantia einm vel essentia Graece οὐσία dicitur, ὅμος unum. Utrumque igitur conjunctum sonat una substantia. Hoc enim vocatur homousion, quod est: Ego et Pater unum sumus, hoc est, ejusdem cum Patre substantiae Sanctus Isidorus Hispalensis, Etymologiae, Liber VII, Caput II Source: Migne PL 82.263d-264a

Emmanuel is from the Hebrew which in Latin means 'God is with us,' certainly because God was born of the Virgin and appeared to men in the flesh, that on earth He open the way of salvation to Heaven. The names of Christ which pertain to the substance of Divinity are: 'God' and 'Lord'. 'God' because of the unity of His substance with the Father, and 'Lord' because of the subservience of created things to Him. And He is God and He is man because He is Word and He is flesh. Whence he is called the 'Doubly Begotten', because the Father begot him without a mother in eternity, and because a mother begot him without a father in time. He is called the 'Only Begotten' according to the excellence of His Divinity, for He is without brothers, and He is called the 'First Begotten' with regard to His assuming human nature by which He deigned to have brothers through the grace of adoption, among whom He was the 'First Begotten'. He is called 'Homousios' because of the unity of substance with the Father. For in Greek substance or essence is called 'ousia' and 'homos' means one. Thus the two joined together mean one substance. So He is called called Homousion, that is, 'I and the Father are one,' 1 that is, He is of the same substance of the Father. Saint Isidore of Seville, The Etymologies Book 7, Chap 2 1 Jn 10.30