But this would mean that God couldn't love until he had created the universe. It would mean that love isn't intrinsic to God. But if Jesus shows us God as he really is, then love is intrinsic to God, and God experiences the obedient love of the Son as well as the love of a Father. Thus there's got to be enough of a distinction in roles within God to allow the relationship of love to exist within him. This sounds rather abstruse, but in fact it has very direct consequences for the Christian life.
Christians believe in grace.
When God calls for us to obey him, he also gives us the ability to obey. In some ideas of God, God is a transcendent being completely separated from humanity. For Christians, God has experienced the kind of love he wants from us, and is inviting us to join him. As God is radically personal, his presence is not an abstract force, but a person. Thus we end up with the Holy Spirit as the third member of the Trinity.