Aaron Taylor, a gradute student in Moral Theology, has written a fine Lenten meditation on Cain and Abel. He writes:
Last night I read the story of Cain and Abel to my children from a Bible reader (a sort of simplified paraphrase of the text). I think the first murder is a fitting thing to recall as we move more deeply into our Lenten struggle. We are weeping for our sins, for our exile from Paradise. But unlike our First Parents, we were born into exile, and the already fallen world is the theatre in which our own sin takes place. As St Macarius the Great writes in his Fifth Homily, ‘The word spoken to Cain by the Creator, that sentence pronounced upon him with an outward meaning, Groaning and trembling and tossed shalt thou be upon the earth (Gen. iv. 12), is a type and likeness of what all sinners undergo in secret.’ 
Patristic interpretations of God’s rejection of Cain’s sacrifice focus on the wickedness of Cain’s heart or his carelessness in choosing his sacrifices. In the ‘Great Letter’, St Macarius writes:
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 with favor on Abel’s sacrifices, but did not regard the gifts of Cain’ (Gn 4:4). This teaches us that everything that is done in fear and in faith is pleasing to God, not that which is done for display and without love. 
But there is another perspective we might take. The Welsh poet, R.S. Thomas, has a second interpretation of Cain’s sacrifices....
Read it all here.
Beware a Different Gospel - Edward F. Lundwall, Jr. I wrote this after a visit from a Seventh Day Adventist teacher who kept mixing the Sabbath observance into the Gospel message. ...
1 day ago