Heavenly mindedness leads to earthly good
Athanasius, if he is known, is best known as a 4th century theologian who fought tooth and nail to insist that there was only one God, yet also that Christians know him as Father, Son and Holy Spirit—God in three persons, the Trinity. In fighting for what seems to non-christians (and sadly, some Christians) like an obscure and impractical doctrine, Athanasius found himself defending the very heart of our salvation and explaining why God the Father sent God the Son into this world:
“For God sent not His Son into the world to condemn the world, but that the world through Him might be saved” (S. John 3:17). All mankind had formerly incurred the sentence of the Law, and were guilty criminals; but the Word of God took upon himself the punishment to be inflicted, and thus justice was satisfied; and, by undergoing punishment in our nature, He applied to our persons the redemption wrought by it. And this was what S. John meant when he exclaimed, “The Law was given by Moses, but grace and truth came by Jesus Christ” (S. John 1:17). How much more excellent is grace than the Law, and how far superior is truth to a shadow of it.
(Orations against the Arians, 1.60)
If the doctrine of the Trinity is an invention; if the Son of God turns out not to be God, this wonderful saving truth collapses. Athanasius saw the glory of our salvation and its basis in God's trinitarian nature, and rejoiced in it.
One way of finding out more about the doctrine of the Trinity is to read chapter 3 of Broughton Knox's book, The Everlasting God, available from Matthias Media.