Natural law refers to God's moral law as revealed through nature—in particular, through God's gift of the human conscience. Christians are more familiar with God's moral law as revealed through Scripture and commonly cite Bible passages when addressing moral issues. However, God's moral law is not uniquely biblical. Whereas the gospel of forgiveness in Christ is uniquely biblical (for God reveals it to us only there), the divine moral law may be discovered also in nature. We appeal to natural law when building a case for our understanding of marriage in the civic sphere, since God has written His moral law in the consciences of all people and created all people with the faculty of reason for discerning these truths of human nature (Romans 2:14-15). The Lutheran Confessions at times also appeal to natural law, natural rights, and the like, even while still maintaining the sola scriptura principle (e.g. Apol. XVI, 11; Apol. XXIII (XI), 6-12, 60). This is possible because natural law, properly construed, will not contradict Scripture. We recognize, of course, the injury that original and actual sin cause to the conscience and human reason, and thus we affirm the need for our consciences to be continuously reformed by the Word of God and for our reason to be taken "captive to Christ" (2 Corinthians 10:5).
By the term "natural family" we mean the family as defined through natural law. We prefer this to the notion of "the traditional family," since we are not basing our definition of family merely on human traditions, but rather on human nature as God created it: God, in the very process of creating the first humans, instituted marriage as a lifelong union between one man and one woman and blessed this institution as the proper sphere for begetting and nurturing children (Gen 1:26-28; 2:18,21-25; LC Sixth Commandment, 207).