What is Zeal?

J.C. Ryle gives us a classic description of zeal when he writes:

Zeal in religion is a burning desire to please God, to do His will, and to advance His glory in the world in every possible way . . .
A zealous man in religion is pre-eminently a man of one thing. It is not enough to say that he is earnest, hearty, uncompromising, thorough-going, whole-hearted, fervent in spirit. He only sees one thing, he cares for one thing, he lives for one thing, he is swallowed up in one thing; and that one thing is to please God. Whether he lives, or whether he dies--whether he has health, or whether he has sickness--whether he is rich, or whether he is poor--whether he pleases man, or whether he gives offence--whether he is thought wise, or whether he is thought foolish--whether he gets blame, or whether he gets praise--whether he gets honour, or whether he gets shame--for all this the zealous man cares nothing at all. He burns for one thing; and that one thing is to please God, and to advance his glory. If he is consumed in the very burning, he cares not for it--he is content. He feels that, like a lamp, he is made to burn . . . (Quoted in J.I. Packer, Knowing God, 173)."