from A TREATISE CONCERNING RELIGIOUS AFFECTIONS

"...There never will, in this world, be an entire purity, either in particular saints, in a perfect freedom from mixtures of corruption; or in the church of God, without any mixture of hypocrites with saints, and counterfeit religion, and false appearances of grace with true religion, and real holiness."
Introduction

"That religion which God requires, and will accept, does not consist in weak, dull, and lifeless wishes, raising us but a little above a state of indifference: God, in his word, greatly insists upon it, that we be good in earnest, 'fervent in spirit,' and our hearts vigorously engaged in religion... It is such a fervent vigorous engagedness of the heart in religion, that is the fruit of a real circumcision of the heart, or true regeneration, and that has the promises of life."
Part I, Ch. II, 1

"...Worldly affections are very much the spring of men's motion and action; so in religious matters, the spring of their actions is very much religious affection: he that has doctrinal knowledge and speculation only, without affection, never is engaged in the business of religion."
Part I, Ch. II, 2

"All who are truly religious are not of this world, they are strangers here, and belong to heaven; they are born from above, heaven is their native country, and the nature which they receive by this heavenly birth, is a heavenly nature, they receive an anointing from above; that principle of true religion which is in them, is a communication of the religion of heaven; their grace is the dawn of glory; and God fits them for that world by conforming them to it."
Part I, Ch. II, 8

"There is much affection in the true saints which is not spiritual; their religious affections are often mixed; all is not from grace, but much from nature. And though the affections have not their seat in the body; yet the constitution of the body may very much contribute to the present emotion of the mind. And the degree of religion is rather to be judged of by the fixedness and strength of the habit that is exercised in affection, whereby holy affection is habitual, than by the degree of the present exercise."
Part I, Ch. II, 10

"There are false affections, and there are true. A man's having much affection, does not prove that he has any true religion: but if he has no affection it proves that he has no true religion. The right way, is not to reject all affections, nor to approve all; but to distinguish between affections, approving some, and rejecting others."
Part I, Ch. III, 1

"The saints and angels in heaven, that have religion in its highest perfection, are exceedingly affected with what they behold and contemplate of God's perfections and works. They are all as a pure heavenly flame of fire in their love and in the greatness and strength of their joy and gratitude: their praises are represented, 'as the voice of many waters and as the voice of a great thunder.' ...it certainly appears, that religious affections being in a very high degree, is no evidence that they are not such as have the nature of true religion. Therefore they do greatly err, who condemn persons as enthusiasts merely because their affections are very high. And on the other hand, it is no evidence that religious affections are of a spiritual and gracious nature, because they are great. It is very manifest by the holy Scripture, our sure and infallible rule to judge of things of this nature, that there are religious affections which are very high, that are not spiritual and saving."
Part II, Ch. I

"That persons are disposed to be abundant in talking of things of religion, may be from a good cause, and it may be from a bad one. It may be because their hearts are very full of holy affections; 'for out of the abundance of the heart the mouth speaketh:' and it may be because persons' hearts are very full of religious affection which is not holy; for still out of the abundance of the heart the mouth speaketh."
Part II, Ch. III

"But with respect to love; it is plain by the Scripture, that persons may have a kind of religious love, and yet have no saving grace."
Part II, Ch. VI