Yesterday I wrote of the role of the Church as teacher (magister) and interpreter of the Scriptures. Today we see another import aspect of the proper interpretation of the word of God, the unity of scripture.
In the gospel Jesus's argument with the Pharisees is ostensible about whether or not it is lawful to pick the grains and eat them on the Sabbath, but this is only on the surface. Underneath is a much more import debate. Who is the proper interpreter of the Law, the Pharisees or Jesus?
As Christians, we would say Jesus. Jesus is the best interpreter of the law because he was the giver of the law. He is God and was there from before the creation of the universe. As so for us, every part of scripture must be examined in light of the gospel. And the Old Testament must be examined first in it's context, then in the light of the Gospel, the words and actions of Jesus.
Again we come back to the question, how do I know the will of God. Yes, we pray for guidance. But we also recall the words of the prophet Jeremiah,
When I found your words, I devoured them; your words were my joy, the happiness of my heart, Because I bear your name, LORD, God of hosts.
Through baptism we bear the name in a way Jeremiah could never imagine. And so we devour in a unique way the gospels. How do I know the will of God? Simple. Always and everywhere I imitate God made man, Jesus Christ.