On The Holy Trinity by St. Augustine
Explains for what the Son of God was sent, viz, that by Christ's dying for sinners, we were to be convinced how great is God's love for us, and also what manner of men we are whom He loved. That the Word came in the flesh, to the purpose also of enabling us to be so cleansed as to contemplate and cleave to God. That our double death was abolished by His death, being one and single. And hereupon is discussed, how the single of our Saviour harmonizes to salvation with our double; and the perfection is treated at length of the senary number, to which the ratio itself of single to double is reducible. That all are gathered together from many into one by the one Mediator of life, viz. Christ, through Whom alone is wrought the true cleansing of the soul. Further it is demonstrated that the Son of God, although made less by being sent, on account of the form of a servant which He took, is not therefore less than the Father according to the form of God, because He was sent by Himself: and that the same account is to be given of the sending of the Holy Spirit.