Sometimes I get a question about ambition in this world, and of course, the New Testament is full of commands to not be enamored with this world, to not be worldly, to not be someone who is in love with the world's systems. But does that mean I can't be ambitious? Or if I am ambitious, does that make me selfish?

Well, first of all, those two terms aren't necessarily mutually exclusive. A Christian can be very ambitious in a godly fashion while being a very selfless person. On the other side, a Christian can also be lazy and have no ambitions whatsoever, which is an extremely high form of selfishness, because that means he doesn't care about providing for his family, doesn't care about people around him, he's not motivated to do anything. So I would say that ambition is actually a form of godliness when it's paired with godly character and a proper perspective of the world.