Quoted in S. Timoshenko’s History of Strength of Materials:
Since the fabric of the universe is most perfect, and is the work of a most wise Creator, nothing whatsoever takes place in the universe in which some relation of maximum and minimum does not appear. Wherefore there is absolutely no doubt that every effect in the universe can be explained as satisfactorily from final causes, by the aid of the method of maxima and minima, as it can from the effective causes themselves…Therefore two methods of studying effects in nature lie open to us, one by means of effective causes, which is commonly called the direct method, the other by means of final causes…One ought to make a special effort to see that both ways of approach to the solution of the problem be laid open; for this not only is one solution greatly strengthened by the other, but, more than that, from the agreement between the two solutions we secure the very highest satisfaction.
Very few people on the earth have contributed to the basics of mathematics and mechanics than Euler. Living in the “Age of Reason” Euler pushed science forward while remaining a Christian all of his life.