by St. Macarius the Great
From Genesis, Creation, and Early Man: The Orthodox Christian Vision, by Fr. Seraphim Rose, edited by Hieromonk Damascene, 2nd ed., p. 292.
I always remember that it was Abel who offered a sacrifice to God of the fat and firstlings of his flock, while Cain offered gifts of the fruits of the earth, but not of the firstfruits. It is said: 'And God looked upon Abel and his gifts, but Cain and his sacrifices He regarded not' (Gen. 4:4-5). This teaches us that everything that is done in fear and in faith is pleasing to God, and not that which is done for display and without love.