This icon is known as Christ's blessing us. Note his two raised fingers. Whenever I explained the Trinity or hypostatic union, I'd show this icon, or one of the many other facsimiles of this depiction of Jesus. Everyone in the class would immediately take out their pen and paper and take notes.
God is one divine being--a hand. He also has two natures, human and divine; that's what the icon is telling you. One God that has two perfectly complete natures--human and divine. This is called the hypostatic union.
The other three fingers represent the Trinity: Father, Son, and Holy Spirit. That explanation has been attempted in other posts.
