In the chapter called "Good Infection" from the fourth book of Mere Christianity by C. S. Lewis, the author furthers his explanations in previous chapters on why God contains three persons but is still only one being. The words making and begetting that he uses have to do with the differences in relationship between God and his created beings (us) and God and his son, Jesus. When God makes something, he creates something different than himself. This includes humans, which are separate creations and not children of God in the same way that Jesus is God's son. Humans are something other than God. In an earlier chapter, Lewis likens humans to statues or pictures of God.
When Lewis writes of begetting, though, he is referring to God creating something of the same kind as himself. According to Lewis, humans beget other humans, but God does not beget humans because the relationship is not the same. However, Jesus is God's son. In Jesus, God has created something that is the same as himself. This is the act of begetting, not making.
Lewis clarifies that though the relationship of father and son is a useful analogy of God and Jesus, it is different from a human father/son relationship in that both God and Jesus have existed for eternity, and one has never been without the other. Jesus has always streamed forth from God "like light from a lamp, or heat from a fire, or thoughts from a mind."
Lewis explains that the phrase "God is love" does not mean that we should worship love as if it was God. This phrase is an acknowledgment of the dynamic relationship between God and Jesus. According to Lewis, if God was alone before he made Jesus, he would not be love, because love is a relationship between at least two people. The activity of love between God and Jesus "has been going on in God forever and has created everything else." The spirit of the eternal union between God and Jesus is so real that it is another person, generally referred to as the Holy Ghost or the Holy Spirit.