The number three is a really interesting number. It is symbolic of completeness or the entirety of something. Some examples are three dimensions, the idea that it takes three planes to create a 3D object. 1D and 2D are incomplete, but 3D is complete. Another example is our divisions of time as past, present and future.
The best biblical example of completeness is the trinity, the triune God, the Godhead three in one. The three entities of God the Father, Jesus the Christ and the Holy Spirit are all one in nature—the complete God in tri-unity, the trinity.
The symbolism of the number three is of completeness, but the meaning comes from the text. In Isaiah 6, the angels “were calling to one another: ‘Holy, holy, holy is the LORD Almighty’” (v. 3 NIV). To be holy is to be set apart, different from everything else. The angels were acknowledging that “the LORD Almighty” was completely set apart from sin, but not only that, but in that they said “Holy, holy, holy,” not simply “holy” says that he was complete, the entirety of sinlessness. This same exact scenario occurs again in Revelations, chapter 4.
This is an analogy for the number three according to the usage in the bible. If you were to jump, you might jump a foot or so off the ground. If you were to jump, jump, you might be able to leap onto the rooftop. But if you were to jump, jump, jump, you would jump so high that you were break the atmosphere of the earth. You would jump so high that you would reach across galaxies. You would jump so high that you would reach the very extent of the universe.