14 But in what does eternity of life consist? His own words tell us:— That they may know You the only true God, and Jesus Christ Whom You have sent. Is there any doubt or difficulty here, or any inconsistency? It is life to know the true God; but the bare knowledge of Him does not give it. What, then, does He add? And Jesus Christ Whom You have sent. In You, the only true God, the Son pays the honour due to His Father; by the addition, And Jesus Christ Whom You have sent, He associates Himself with the true Godhead. The believer in his confession draws no line between the Two, for his hope of life rests in Both, and indeed, the true God is inseparable from Him Whose Name follows in the creed. Therefore when we read, That they may know You, the only true God, and Jesus Christ Whom You have sent, these terms of Sender and of Sent are not intended, under any semblance of distinction or discrimination, to convey a difference between the true Godhead of Father and of Son, but to be a guide to the devout confession of Them as Begetter and Begotten.
Source: On the Trinity (New Advent)