St. (Padre) Pio said that he was just "a monk who prayed" and that prayer is our only weapon....St. Therese on that subject courtesy Amy Welborn.
Our Dominican priest had much to say last night on the OT/NT connections..
1) Cain offered God 'the fruits of the earth' - i.e. bread and wine - which God rejected. Abel offered the perfect sacrifice (unblemished lamb), acceptable to God. We re-enact this when we go to Mass, admitting we are Cains by bringing up at the Offertory the fruits of the earth, but after the Consecration we offer the unblemished Lamb (Christ). If the Eucharist is just a symbol (i.e. bread and wine) then we are offering what God rejected in the OT.
2) In the OT, the image of the serpent healed the snakebit. In the NT, Jesus in the form of man, "made sin for us", heals us.
3) John's gospel promises that God will teach us the Scriptures. There is great freedom in the gospels. "But there are also many other things which Jesus did; were every one of them to be written, I suppose that the world itself could not contain the books that would be written." (John 21:25) The catechism exists as boundary, to warn us from areas the Church has proven not to be fruitful.
Abel's blood "cried out for vengeance" while Christ's blood cries out for mercy.