Again Celsus proceeds: “If you should tell them that Jesus is not the Son of God, but that God is the Father of all, and that He alone ought to be truly worshipped, they would not consent to discontinue their worship of him who is their leader in the sedition. And they call him Son of God, not out of any extreme reverence for God, but from an extreme desire to extol Jesus Christ.” We, however, have learned who the Son of God is, and know that He is “the brightness of His glory, and the express image of His person,” and “the breath of the power of God, and a pure influence flowing from the glory of the Almighty;” moreover, “the brightness of the everlasting light, the unspotted mirror of the power of God, and the image of His goodness.” We know, therefore, that He is the Son of God, and that God is His father.
And there is nothing extravagant or unbecoming the character of God in the doctrine that He should have begotten such an only Son; and no one will persuade us that such a one is not a Son of the unbegotten God and Father. If Celsus has heard something of certain persons holding that the Son of God is not the Son of the Creator of the universe, that is a matter which lies between him and the supporters of such an opinion. Jesus is, then, not the leader of any seditious movement, but the promoter of peace.
For He said to His disciples, “Peace I leave with you, My peace I give unto you;” and as He knew that it would be men of the world, and not men of God, who would wage war against us, he added, “Not as the world gives peace, do I give peace unto you.” And even although we are oppressed in the world, we have confidence in Him who said, “In the world you shall have tribulation; but be of good cheer, I have overcome the world.” And it is He whom we call Son of God— Son of that God, namely, whom, to quote the words of Celsus, “we most highly reverence;” and He is the Son who has been most highly exalted by the Father.
Grant that there may be some individuals among the multitudes of believers who are not in entire agreement with us, and who incautiously assert that the Saviour is the Most High God; however, we do not hold with them, but rather believe Him when He says, “The Father who sent Me is greater than I.” We would not therefore make Him whom we call Father inferior— as Celsus accuses us of doing— to the Son of God.
Source: Against Celsus (New Advent)