In the beginning of the Old Testament, we read "And God said, Let there be light: and there was light." It appears in this verse that God caused light to appear through the use of language. How can language cause the world to change? What would reality have to be like for the language to change reality?
Direction of fit
To explore these questions, I want to introduce the concept of direction of fit. Direction of fit refers to the relationship between words and reality. In many cases, words can be used to fit the way the world is. These cases have a " word-to-world direction of fit". In other cases, the world changes in order to fit the words that we use. These cases have a "world-to-word direction of fit". These distinctions will be clearer as I describe the possible uses of language.
5 types of speech acts
There are 5 and only 5 things that can be done with language. There are assertives, expressives, directives, commissives, and declarations. These uses of language are called speech acts. Assertives state the way the world is and thus have the word-to-world direction of fit. Assertives refer to statements, descriptions, classifications, explanations, and clarifications. Eg: "The earth rotates around the sun". Expressives do not have a direction of fit but they rely on presuppositions that do have a direction of fit. Eg: "Thank you for passing the guacamole" (which presupposes that the hearer did in fact pass the guacamole).
Directives, commissives, and declarations all have a world-to-word direction of fit. Directives change the world by causing the hearer to do something. Directives include orders, commands, requests and refer to pleading, begging, praying, insisting, and suggesting. Eg: "Go to your room." Commissives change the world by committing the speaker to do something. Commissives refer to vows, threats, pledges, guarantees, contracts, promises, covenants, and oaths. Eg: "I promise to uphold the constitution." Declaratives actually have a dual direction of fit. They change the world by representing the world as being so changed. Eg: "This meeting is adjourned," or, "I now pronounce you husband and wife." A declaration can fail if no one recognizes the declaration. For instance, if I declare that a meeting is adjourned, and the meeting just keeps going on because no one recognizes my speech act, then I have failed to change reality. Therefore declarations are dependent on collective recognition if they are to actually change the world. For a more slightly more thorough introduction to speech acts, check out this post.
Let there be light
So what type of speech act is the utterance, "Let there be light"? It doesn't have a word-to-world direction of fit so it cannot be an assertive. It does not seem to be expressing an emotion that assumes another fact so it cannot be an expressive. It doesn't commit the speaker to a specific action so it is not a commissive. The only possibilities left are directives and declarations, or it might not be a speech act at all. I will examine each of these remaining possibilities.
Is it a declaration?
If the speech act, "let there be light" is a declaration, then God is changing the world by representing it as being so changed. However, when human beings make a declaration they can only change social reality. For example, the declaration, "This note is legal tender for all debts public and private" only applies to the status function of money which is a social fact that requires collective recognition. Human beings cannot change the brute facts of reality through declarations alone. For example, we cannot change reality by saying, "I hereby declare that I am a billionaire." Nor can we change reality by declaring something like, "Let there be good weather." No amount of collective recognition is going to change those brute facts because beliefs alone cannot cause anything to happen without physical action. If the utterance "let there be light" is a declaration, then I cannot make sense it for the reasons just stated. It would presuppose a type of metaphysical idealism which I believe is self-contradictory.
Is it a directive?
Directives are supposed to change the world by causing the hearer to perform some action. The utterance "Let there be light" could be a command to the light itself or it could be a command to an unspecified hearer who is being commanded to create the light through the use of some sort of light-generating technology. If light could be commanded, then that would imply that light has some sort of conscious awareness such that it could understand the meaning of the words and volitionally respond to the directive. In Helaman 12: 8-22, it seems as though Nephi is suggesting that matter obeys God's word which seems to imply that it is conscious. Orson Pratt is said to have more explicitly supported this hylozoistic view. However, I think there is enough room for interpretation to question this interpretation of the scriptures. If light does not have conscious awareness, then some unspecified hearer such as an angel turned on the light after being commanded by God.
Maybe it isn't a speech act at all
The last possibility is that the phrase, "Let there be light" is not a speech act at all but just a soundwave that triggers a preprogrammed event that causes the lights to turn on. For example, when I ask Siri (on my iPhone) to launch an app, I say something like "launch Angry Birds." But the meaning of my words did not cause Siri to open the app. It was merely the soundwave that caused Siri to open the app. Siri could have been programmed to launch the app when it heard the soundwave, "Do NOT launch Angry Birds". Or it could have been programmed to launch the app when it heard the sound wave, "Boom Shakalaka!" Likewise some light generating technology could have been preprogrammed to respond to God's words. It could have been programmed to respond to a particular vibration of his vocal cords, or some bodily movement, or perhaps the technology could have responded to some form of thought detection.
Conclusion
In this post, I have not been as interested in what God caused to be with His words. I am more interested in how God uses words to cause things to be. Understanding how words can change reality can give us insights into the metaphysical nature of reality. Using the example of light, God's words could have been a declaration, a directive, or they could have been a soundwave that triggers a non-volitional technology. In my opinion, it doesn't make sense that the words could be a declaration for the reasons stated above. I am also skeptical of the speech-as-a technology-trigger explanation because I am not aware of any example where God's words are used this way. Intuitively, it does not seem Godlike for God's words to not have any meaning in this way. Therefore, I believe that the utterance, "Let there be light" was a directive. Either matter volitionally obeyed God's words or God was commanding another volitional being (or beings) to cause a series of events to take place in order for earth to have light.
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Scriptures about the power of God's words: Jacob 4:9 Helaman 12:7-21 1 Ne. 17:46