Why was Galileo Galilei called a man of extraordinary will?

Albert Einstein characterizes the great Italian physicist, mechanic, astronomer, philosopher, mathematician Galileo Galilei with his extraordinary human will, intelligence, courage.

Living and working under the conditions of the strongest power of the church, its anti-scientific dogmas, the threat of the inquisition, persecution, until his last days he defended his scientific rational objective views on space, affirming the heliocentric world system, considering the Universe as a giant mechanism with its constant movement.