Each member of your family has been cleaning up different areas of your home, but all the sponges look the same. You squeeze each sponge to see what comes out. As you squeeze the first sponge, you see that cola comes out, and so you decide that someone cleaned the kitchen with that one. Upon squeezing the second sponge, you find tub and tile cleaner - that one was used to clean the bathroom. As you lay the last one down, you look again at their similarity - and they all look the same until they're squeezed.
Christians are the same way.