There is nothing that belongs to Christian experience that is more liable to a corrupt mixture than zeal; though it be an excellent virtue, a heavenly flame, when it is pure: but as it is exercised in those who are so little sanctified, and so little humbled, as we are in the present state, 'tis very apt to be mixed with human passion, yea, with corrupt hateful affections, pride and uncharitable bitterness, and other things that are not from heaven but from hell. (Jonathan Edwards, Thoughts Concerning the Revival, in Yale ed. of Works of Jonathan Edwards, 4:460)
I'm wrapping up a dissertation arguing, in essence, that the Apostle Paul, based on Rom 10:2, Gal 1:14 and Phil 3:6, would agree with that statement.
In a 1743 letter to Thomas Prince in Boston, Edwards put it this way: the degree of grace is by no means to be judged of by . . . the degree of zeal. (ibid., 556)