50 But He proves abundantly that His will is free by the words, As the Father raises the dead and quickens them, even so the Son also quickens whom He will. When the equality of Father and Son in power and honour is indicated, then the freedom of the Son's will is made manifest: when Their unity is demonstrated, His conformity to the Father's will is signified, for what the Father wills, the Son does. But to do is something more than to obey a will: the latter would imply external necessity, while to do another's will requires unity with him, being an act of volition.
In doing the will of the Father the Son teaches that through the identity of Their nature His will is the same in nature with the Father's, since all that He does is the Father's will. The Son plainly wills all that the Father wills, for wills of the same nature cannot dissent from one another. It is the will of the Father which is revealed in the words, For this is the will of My Father, that every one that beholds the Son and believes in Him, should have eternal life, and that I should raise Him up at the last day. Hear now, whether the will of the Son is discordant with the Father's, when He says, Father, those whom You have given Me, I will that where I am they also may be with Me. Here is no doubt that the Son wills: for while the Father wills that those who believe in the Son should have eternal life, the Son wills that the believer should be where He is.
For is it not eternal life to dwell together with Christ? And does He not grant to the believer in Him all perfection of blessing when He says, No one has known the Son save the Father, neither has any known the Father save the Son, and he to whomsoever the Son wills to reveal Him? Has He not freedom of will, when He wills to impart to us the knowledge of the Father's mystery? Is not His will so free that He can bestow on whom He will the knowledge of Himself and His Father? Thus Father and Son are manifestly joint Possessors of a nature common to Both through birth and common through unity: for the Son is free of will, but what He does willingly is an act of the Father's will.
Source: On the Trinity (New Advent)