“For the first time science and medicine can diminish drudgery and pain.
Only those who see the invisible can do the impossible.”

Though sometimes quoted as if he were author of it, the expression "Only those who see the invisible can do the impossible" is one that greatly predates Lown's use of it; it has also been attributed to Thomas Jefferson, Jesus and Mrs. Charles E. Cowman, but the earliest published expression yet located seems to have been one by American Baptist minister Rev. Robert Stuart MacArthur in Royal Messages of Cheer and Comfort Beautifully Told (1909) edited by Sarah Conger Robinson, p. 58
A Prescription for Hope (1985)
Context: We must hold fast to the dream that reason will prevail. The world today is full of anguish and dread. As great as is the danger, still greater is the opportunity. If science and technology have catapulted us to the brink of extinction, the same ingenuity has brought humankind to the boundary of an age of abundance.
Never before was it possible to feed all the hungry. Never before was it possible to shelter all the homeless. Never before was it possible to teach all the illiterates. Never before were we able to heal so many afflictions. For the first time science and medicine can diminish drudgery and pain.
Only those who see the invisible can do the impossible. But in order to do the impossible, in the words of Jonathan Schell, we ask "not for our personal survival: we ask only that we be survived. We ask for assurance that when we die as individuals, as we know we must, mankind will live on".