"Law is twofold -- natural and written. The natural law is in the heart, the written law on tables. All men are under the natural law." - St Ambrose
Gospel text (Mk 2,23-28):
As Jesus was passing through a field of grain on the sabbath,
his disciples began to make a path while picking the heads of grain.
At this the Pharisees said to him,
"Look, why are they doing what is unlawful on the sabbath?"
He said to them,
"Have you never read what David did
when he was in need and he and his companions were hungry?
How he went into the house of God when Abiathar was high priest
and ate the bread of offering that only the priests could lawfully eat,
and shared it with his companions?"
Then he said to them,
"The sabbath was made for man, not man for the sabbath.
That is why the Son of Man is lord even of the sabbath."
Today, as yesterday, Jesus has to contend with the Pharisees, who are distorting Moses' Law, by highlighting the letter of the law while ignoring the actual spirit of the Law. To work, forgive, correct, attend Mass on Sundays, take care of sick people, abide by the commandments..., do we do it because we have to or because of our love for God?
Several times in the Gospels Jesus asks those who had spent years studying the Scriptures if they've never read a certain passage (see e.g. Mk 2:25; Mt 21:16, 42; 22:31). Jesus, of course, knew His hearers had indeed read those passages before. However, He also knew they had not grasped the full meaning of the passage, despite having possibly read it many times.
What about us? Like the Pharisees in today's passage, some of us have devoted years of our lives studying the Scriptures. Yet there are always deeper levels of meaning in the Word of God not yet open to us. Are we content with our current understanding of the Bible? Jesus longs to open our minds to the understanding of the Scriptures (see Lk 24:45), but we must desire understanding and wisdom. It's hard for Jesus to open if we don't bother to knock. Jesus says: "Knock, and it will be opened to you" (Mt 7:7).
Stay rooted in God's Word. Read and study it daily (Acts 17:11). Beg the Lord for an ever deeper desire to sit with Him and listen to His word (Lk 10:39). Whenever possible, read the daily Scriptures at Mass and at Eucharistic Adoration in the presence of Jesus, the Living Word (Heb 4:12), Who will unlock His word for you.
God knows that we are flawed, that we make mistakes, that we sometimes have unholy intentions — but Jesus waits there to save us nonetheless. Salvation lies there as a gift for us to accept. None of us is truly worthy (even the great king David was a deeply flawed human being, and many of the Psalms are surely anthems to his regrets for his sins), but Jesus waits for us patiently.