Jeremiah 17:9

The heart is deceitful, &c.— This passage, divided from the context, and considered as an independent proposition, has been applied in a sense different from the design of the author. This will evidently appear, if we consider the connexion, and the general reason that he is pursuing: for, in the 5th verse, God is introduced as denouncing a woe against all those who fix their ultimate dependence on human power and policy. In the 7th and 8th verses are described the wisdom and happiness of trusting in the Lord, and making him our strength. Then follows the verse that we are considering, which by all the rules of good interpretation (since there is not the least mark of the prophet's beginning a new topic of discourse) must be referred to the same argument, and contain another strong reason against making man our confidence. The heart is deceitful, &c. that is to say, "There may be infinite devices and subtleties in the hearts of men, which thou canst not understand: while they promise thee fair, and make the warmer protestations of affection and zeal for thy service their intentions may be contrary, and their views private and selfish: their resolutions are fickle and mutable, and many little circumstances may prevail with them to change their purposes, and so render their promises vain and delusory. Nay, it is possible for them to arrive at such a pitch of premeditated and desperate wickedness, as to endeavour, even under friendly pretences, to undermine thy interest. Place not, therefore, thy supreme and ultimate confidence in man; but repose it in the unchangeable God; who, as by reason of the perfect and necessary rectitude of his nature, he cannot deceive thee; so, as he is absolute Lord of the universe, and the uncontrollable disposer of all events, he must be able with ease to effect every thing which is necessary for thy security and happiness." See Foster's Sermons, vol. 1: p. 272.