This is a follow on to my earlier post: Two Levels of Right and Wrong
I'm sure I don't need to go into too much detail explaining how God is righteous and holy, and that He ultimately sets the standard for what is right and wrong. In fact the scriptures state that not only is He perfectly righteous and good, but if He were to deviate from this just a little, He would cease to be God (Alma 42: 13, 22, 25; Morm. 9: 19). Of course there is no chance of that ever happening (his goodness and righteousness wouldn't allow it), so we're all safe.
Since God wants us to become like Him in all of His attributes and perfection (Moses 1: 39) He has given us His law to guide us (Prov. 6: 23; 3 Ne. 15: 9). This is why I consider God's Law the foundation of all right and wrong.
His laws also go beyond mere morality. Since He created the world, all of creation follow the laws He ordained from the beginning (including fundamental laws like gravity and electro-magnetism) (D&C 88: 13). It would make no more sense to try to live a good life while disregarding God's moral laws, than it would be to try to build a computer while disregarding the laws of electro-magnetism. All goodness and blessings come only from following God's laws (D&C 130: 20-21). As Alma clearly taught, "wickedness never was happiness." (Alma 41: 10).
So how do we find out God's laws? The scientific method has been very effective at identifying the laws God uses to govern the physical world, but hasn't been quite as effective at identifying God's moral laws. (In my opinion that's why the physical sciences tend to progress further and faster than the social sciences.) While we are spiritual creatures, we're living in a fallen and carnal world. Without God's direct involvement, I doubt we'd even be able to properly frame the necessary questions much less identify the answers. We'd be "ever learning, and never able to come to the knowledge of the truth" (2 Tim. 3: 7).
This is precisely why God has declared His law to mankind through prophets (Jer. 35: 15; Mosiah 3: 13; Moses 5: 58). This law has then been preserved for us in the Scriptures. The Old Testament records God's dealing with mankind from the creation to before the coming of Christ. While it was geared most specifically towards the Children of Israel, it is the foundation upon which are other scriptures are build (i.e., all other scriptures assume you have an understanding of the Old Testament.) It's probably the most widely accepted book of scripture in the world today and formed the basis of just about all modern law and government.
The New Testament records the fulfillment of the Law of Moses by Christ. It's teachings build upon the Old Testament, and it provides further understanding of how it's necessary to center your life on Christ. While it teaches that the actual practices of the Law of Moses are no longer necessary, the righteous principles that under-girded the Law of Moses still apply. All who accept Jesus Christ as their Lord and Savior are obligated to accept the Old and New Testament (the Bible) as authoritative.
Finally, in our day God has provided further guidance and direction with the Book of Mormon, Doctrine and Covenants, and the Pearl of Great Price. These books of scripture are meant to clarify and expand on the teachings of the Bible. All who have come to accept the Church of Jesus Christ of Latter-day Saints as Christ's restored church on earth today, and have joined it through baptism, are bound follow the teachings found in all these scriptures.
In short, God has given us the Scriptures to be a guide in this life. It is His law as contained in the scriptures that are binding and authoritative (D&C 42: 59). Any teaching, doctrine, or guidance must be found in the scriptures, or they're not binding on us as a whole. There is also only one person on the earth who has been authorized to add, delete, or modify what's spelled out in the scriptures: God's ordained prophet (D&C 43: 2-6). If it comes from anyone else, you can be assured that it's not authoritative or binding, even if it may be true. (If it is true, but hasn't yet been revealed to the Church through the Prophet, that person should have kept it to themselves in accordance with Alma 12: 9.)
The Scriptures don't speak kindly of those who would try to supplant God's words with their own. Whether it's false prophets (Jer. 14: 14-15), false teachers (2 Pet. 2: 1), or people using their own standard for judgment instead of what the Lord has given (James 4: 11-12), the result is not good. That is why it is so important to diligently search the scriptures ourselves. Not only does this help us know how to best govern our own lives, but it helps us to identify false teachers who misinterpret or go beyond what is actually written.
[I've heard people try to use D&C 1: 38 and D&C 68: 4 to argue that the teachings of any church leader given in an official capacity are scripture and binding. However, these scriptures need to be read in light of D&C 43: 2-6, referenced above. Their teachings are scripture when they're proclaiming the gospel by "reasoning with and expounding all scriptures unto them," (D&C 68: 1) not making up brand new scripture. For more information this statement by the Church or this talk by J. Reuben Clark, Jr. can be useful. I'll have more to say about it in my next post.]
In summary, God's Law provides the ultimate source of right and wrong. While it may be binding only to those who have made covenants with Him, it's still very beneficial for all people. The Scriptures contain the portion of His law that He expects all of us to follow. If anyone tries to teach you something that can't be found in the Scriptures, you can be assured it isn't from God (unless that person is His ordained Prophet and he's acting in that capacity.) This forms the baseline from which everything else is established.
The next level of right and wrong, which comes into play where the Scriptures are silent, is your own individual conscience as guided by the Holy Ghost. That will be the subject of my next post.