Hebrews 3:12

Take heed, brethren - In view of the conduct of the rebellious Jews, and of their fearful doom, be on your guard lest you also be found to have had the same feelings of rebellion and unbelief. See to it, that under the new dispensation, and in the enjoyment of the privileges of the gospel, you be not found to manifest such feelings as shall exclude you from the heavenly world. The “principle” has been settled by their unbelief that they who oppose God will be excluded from his rest. That may be shown under all dispensations, and in all circumstances, and there is not less danger of it under the gospel than there was when the fathers were conducted to the promised land. You are traveling through a wilderness - the barren wilderness of this world. You are exposed to trials and temptations. You meet with many a deadly and mighty foe. You have hearts prone to apostasy and sin. You are seeking a land of promise; a land of rest. You are surrounded by the wonders of Almighty power, and by the proofs of infinite beneficence. Disobedience and rebellion in you will as certainly exclude you from heaven as their rebellion did them from the promised land; and as their great sin was unbelief, be on your guard lest you manifest the same.

An evil heart of unbelief - An evil, unbelieving heart. The word “unbelief” is used to qualify the word “heart,” by a Hebraism - a mode of speech that is common in the New Testament. An unbelieving heart was the cause of “their” apostasy, and what worked their ruin will produce ours. The root of their evil was “a want of confidence in God” - and this is what is meant here by a heart of unbelief. The great difficulty on earth everywhere is a “want of confidence in God” - and this has produced all the ills that man has ever suffered. It led to the first apostasy; and it has led to every other apostasy - and will continue to produce the same effects to the end of the world. The apostle says that this heart of unbelief is “evil.” Men often feel that it is a matter of little consequence whether they have faith or not, provided their conduct is right; and hence, they do not see or admit the propriety of what is said about the consequences of unbelief in the Scriptures. But what do they say about a want of confidence between a husband and wife?

Are there no evils in that? What husband can sleep with quietness on his pillow, if he has no confidence in the virtue of his wife? What child can have peace who has no confidence in a parent? How can there be prosperity in a community where there is no confidence in a bank, or an insurance office, or where one merchant has no confidence in another; where a neighbor has no confidence in his neighbor; where the sick have no confidence in a physician, and where in general all confidence is broken up between man and man? If I wished to produce the deepest distress in any community, and had the power, I would produce the same want of confidence between man and man which there is now between man and his Maker. I would thus take away sleep from the pillow of every husband and wife; every parent and child; and make every man wretched with the feeling that all the property which he had was insecure. Among people, nothing is seen to be productive of greater evil than a want of confidence or faith - and why should not the same evil exist in the divine administration? And if want of confidence produces such results between man and man, why should it not produce similar, or greater, miseries where it occurs in relation to God? There is not an evil that man endures which might not be alleviated or removed by confidence in God; and hence one great object of the Christian religion is, to restore to man his lost confidence in the God that made him.

In departing from the living God - Manifested in departing from him; or leading to a departure from him. The idea is, that such a heart of unbelief would be connected with apostasy from God. All apostasy first exists in the heart, and then is manifested in the life. They who indulge in unbelief in any form, or in regard to any subject, should remember that this is the great source of all alienation from God, and that if indulged it will lead to complete apostasy. They who wish to live a life of piety should keep the heart right. He that lives “by the faith of the Son of God” is safe; and none is safe but he.