1) When Christians argue that God is the ground of morality, they are not arguing that a revelation from God –the Bible, for example – is necessary to ground morality. Nor are they arguing that we need the Bible to have moral knowledge. That would be a strange position for the Christian to take. Romans 2 and 1 Corinthians 5 assume that believers and unbelievers can have moral knowledge without knowing the Scriptures; and these passages also assume that unbelievers can be more moral than believers!
2) The point of the moral argument is not that atheists cannot have moral knowledge or a moral code. Rather, the concern is that atheism cannot explain the existence of moral values and obligations. To illustrate, I might know that positrons exist by reading a few science textbooks. But because I am not a trained physicist, I lack the knowledge to explain why they exist.
3) While we bring our own moral beliefs to Scripture, Scripture challenges and corrects many of our moral convictions. For example, when we understand the Bible’s teaching on the importance of sacrificial love deepens our understanding of that virtue. The scriptural call for a pure heart, the intensity of God’s holiness and the need for forgiveness leads us to abandon any belief in our own self-righteousness, repent to God and trust in Jesus.
4) When we read the Old Testament law codes, we must remember that ancient Near Eastern society did not have a modern penal system! Bureaucrats did not take written records of legal precedents; prisons, in the modern sense did not exist. The laws were tough, to enforce an orderly society. The death sentence is often permitted, but it only seems to be mandatory in the case of murder. However, these laws were to be applied with wisdom, mercy and compassion. Indeed, the prophetic tradition challenges the heartless application of God’s law. The elders who applied the Old Testament laws had much more scope for interpetation and application than contemporary officials.
5) The Bible is inerrant and infallible - but it is not a “how to” guide for every ethical dilemma. We cannot flick through its pages to find a proof text for every decision. To be sure there are absolute commands – lust and adultery are always forbidden, for example. But there is wisdom and advice also - it is better to show mercy than to perform tedious religious rituals. There are characters to emulate – above all Jesus – and narratives to inspire. When we read the Bible our overall aim must be to become the sort of person God wants us to be. We do not read to update our databanks; we read to change who we are.