Harden not you hearts
There is a natural hardness of the heart; the heart of man is like a stone, destitute of spiritual life, motion, and activity; it is senseless, stupid, impenitent, stubborn, and inflexible, on which no impressions can be made, but by powerful grace: and there is an acquired, habitual, and voluntary hardness of heart, to which men arrive by various steps; as entertaining pleasing thoughts of sin; an actual commission of it, with frequency, till it becomes customary, and so habitual; an extenuation or justification of it, and so they become hardened against all reproofs and sermons, and to all afflictions and judgments; are insensible and past feeling, and openly declare for sin, and glory in it: and there is a hardness which God's people are liable to, and should guard against; and which is brought on by a neglect of private and public worship, and by keeping bad company, and through the ill examples of others, and by giving way to lesser sins; for all sin is of an hardening nature:
as in the provocation, in the day of temptation in the wilderness;
the Jews provoked God in the wilderness by their unbelief, murmurings, ingratitude, and idolatry; and they tempted him there by distrusting his power and goodness; hence one of the places in which they murmured against him was called Massah and Meribah, ( Exodus 17:7 ) and it is an aggravation of their sin, that it was in the wilderness, after they had been just brought out of bondage into liberty, and had lately had such an instance of the power and goodness of God, in bringing them through the Red sea; and where they could have no human supplies, and therefore should have been entirely dependent on God, and trust in him.