Thomas Aquinas teaches that in addition to the eternal law, the natural law, and the positive law, there is also the ‘divine law.’ The natural law is intended to be for all humans, everywhere. By following the dictates of the natural law it is possible for us to live happy lives here on earth. The divine law is also intended to be for all humans, everywhere. Obeying the divine law, however, is a course of action that equips us to go beyond a merely earthly happiness. Persons who seek to obey God and honor His commands can obtain a supernatural end – an afterlife of eternal happiness in heaven.
Aquinas divides the divine law, or special revelation from God, into two kinds: old and new. The new divine law corresponds to the new covenant, or ‘New Testament.’ The old divine law corresponds to the old covenant or ‘Old Testament.’ Following the dictates of the old covenant was the way that the Israelites were once taught to obey God in the Old Testament. The new divine law, or new covenant, has now replaced the old covenant. Today, believing in the salvation work of Jesus Christ is the way Christians are taught to obey God and achieve eternal happiness.
Aquinas’s distinction between the old and new divine laws raises a perplexing question. Since Christians now live under the terms of the ‘new’ divine law, what ought to be our attitude toward the old divine law? Should we continue to obey the 10 Commandments and the various other ordinances of the Mosaic law? Or should we just throw it all aside and say that it is no longer of any importance for our day-to-day lives?
Instead, most Christian philosophers have argued that there are today at least three uses of the ‘old’ divine law, or Mosaic law:
1) To curb our sinful desires and promote life in society: the old law serves all of humanity by restraining our sin and by setting up ethical boundaries to organize our lives in society. This enables humans to enjoy a certain measure of order and justice in their lives. Revering the old law and making some effort to embody its ideals in our lives is a way for us to restrict the growth of sin in our souls.
2) To mirror Christ and instruct us in our sinfulness: another use of the old law is as a tool of the Holy Spirit to show us our sin. The law makes us sorrowful about our sin, shows us our need for help from outside, and, ultimately, prepares us to accept Christ as our savior. The old law is intended to be a manifestation of God’s character and to show us how sinful we are, in contrast to God’s righteousness. Its presence in our lives shows us our need for the mercy and grace of Christ.
3) To guide us and sanctify us: still another use of the old law is that it teaches us, positively, how to live good moral lives. Although not all of its dictates are immediately relevant for our lives today (e.g. think of its many dietary restrictions), nevertheless the principles that it embodies are just good ideas for Christians to follow in their day-to-day activities (i.e. moderation in our eating habits, etc.). Following the principles that are embodied in the old law is a blueprint for us to become sanctified and to learn to follow God in more meaningful ways.