Virtually every instance of the expression "imaginations of the heart" in the Bible likens such imaginations with idolatry and following other gods. At a covenant ceremony, Moses warns Israel, "Lest there should be among you a man, woman, family or tribe whose heart turns away this day from the Lord our God to go and serve the gods of these nations; lest there should be among you a root that bears gall and wormwood" (Deut. 29:18). Moses cites a classic kind of self-deception, at the same time harking back to the curses he has just enumerated in connection with the covenant: "And it come to pass, when he hears the words of this curse, that he bless himself in his heart, saying, I shall have peace (salvation), though I walk in the imagination of my heart, to add drunkenness to thirst" (Deut. 29:19).
Moses thereby gives us to understand that self-deception, or "drunkenness," follows a personal lack of "thirst" for the knowledge of God. Paul concurs with that interpretation. He says that imaginations--or reasonings and rationalizations--are a kind of conceit or pretense that exalts itself "against the knowledge of God" (2 Cor. 10:5). Moses thus concludes his warning by showing how the Lord will not withhold his anger and jealousy from such but will bring "all curses that are written in this book" upon them, separating them unto evil from his covenant people, blotting out their names from under heaven (Deut. 29:20-21).
Imaginations of the heart are nonetheless something each of us has to live with. They are an integral part of being mortal, expressing a person's innate disposition to think or to do evil. Unavoidably, "the imagination of man's heart is evil from his youth" (Gen. 8:21). People possess a natural tendency to be proud, mischievous, and wicked (Prov 6:18; Luke 1:51). But when they let the imaginations of their heart rule them, when they do not make captive every thought in obedience to Christ (2 Cor. 10:5), then they fall. Then, though "they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened" (Rom. 1:21).
When the Lord's prophet calls on the people to repent, they think, "There is no hope"--they continue following their own devices, relying for guidance on the imaginations of their heart (Jer. 18:12). Instead of hearkening to the Lord's counsel, they hearken to those who say, "Ye shall have peace.... No evil shall come upon you" (Jer. 23:17). In the end, the Lord esteems such people as good for nothing and vents his wrath upon them (Jer. 13:10-14). Biblical types of falling prey to the imaginations of the heart include the people before the Flood, the people at the Tower of Babel, and the nations of Israel and Judah before the Exile.
Nephi identifies the large and spacious building he and has father saw in vision as the "vain imaginations and the pride of the children of men" (1 Nephi 12:18). Nephi notes that a great and terrible gulf--the justice of the eternal God--divides those in the building from the godly (1 Nephi 12:18). Those who gather in the building include not only non-Israelites but also members of the house of Israel, who mock, scorn and fight their humble brethern (1 Nephi 8:27, 33; 11:35).
One thing that distinguishes the great multitude in the building is the exceeding fine manner in which they dress (1 Nephi 8:27). Their sophistication and finger-pointing reflect a preoccupation with unreality, as the building in the air, standing high above the earth, also signifies (1 Nephi 8:26). The building's fall is the destruction of all wicked nations, kindreds, tongues, and people--an event of the last days (1 Nephi 11:36).
In the days of Noah "God saw that the wickedness of men had become great in the earth, and every man was lifted up in the imagination of the thoughts of his heart, being only evil continually" (Moses 8:22), a particular type of evil that also exists in these last days, even among those who "have professed to know my name and have not known me" (D&C 112:26).
By engaging in self deception, basing our behavior on false pretenses, we sell ourselves short of divine blessings. We endanger our lives as we face perilous times, denying the good effect of God's enduring love for us.
In summary, in the last days, those of us who seek not the Lord to establish his righteousness, but walk every one in our own way, after the image of our own god--whose image is the likeness of this world, whose substance is that of an idol--must face the consequences of our actions: must perish in Babylon, which shall fall (D&C 1:16).
Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. Professing themselves to be wise, they became fools, and changed the glory of the uncorruptible God into an image made like to corruptible man.... Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator.... (Romans 1:21-23;25)