No sin is more apt to insinuate itself into our hearts, and duties, than hypocrisy.

We, of all men, are most in danger to be deceived by it: For our employment lying in, and about spiritual things, we are, on that account, stiled spiritual men (Hosea 9:7). But it is plain, from that very place, that a man may be objectively a spiritual, and all the while subjectively a carnal man. Believe it, brethren, it is easier to declaim, like an orator, against a thousand sins of others, than it is to mortify one sin, like Christians, in ourselves; to be more industrious in our pulpits, than in our closets; to preach twenty sermons to our people, than one to our own hearts.

—John Flavel
The Whole Works of the Reverend John Flavel, 6:568.