The apostle Paul claimed the Law is written on the 'fleshy tables' of the human heart (2 Cor. 3:3 KJV). What he meant are these 'shoulds' and 'shouldn'ts' are both instinctual and inescapable, part of our DNA. They are a psychological reality. We may justify our actions away, but deep down, we know when we've done something wrong.
The hub of Christianity is not 'do something for Jesus.' The hub of Christianity is 'Jesus has done everything for you.' And my fear is that too many people, both inside and outside the church, have heard our pleas for intensified devotion and concluded that the focus of Christian faith is our love for God instead of God's love for us. Don't get me wrong--what we do is important. But it is infinitely less important than what Jesus has done for us.
One-way love is rare, though, and it always comes as a surprise. Fortunately, the glimpses we receive in relationships are only a foreshadowing of God's love for us. They are like little arrows that point to the very heart of the universe, what Dante called 'the Love that moves the Sun and the other stars,' the love that received its fullest expression in the person and work of Jesus Christ.
The Bible is not a witness to the best people making it up to God; it's a witness to God making it down to the worst people. Far from being a book full of moral heroes whom we are commanded to emulate, what we discover is that the so-called heroes in the Bible are not really heroes at all. They fall and fail; they make huge mistakes; they get afraid; they're selfish, deceptive, egotistical, and unreliable. The Bible is one long story of God meeting our rebellion with His rescue, our sin with His salvation, our guilt with His grace, our badness with His goodness.