What does the Bible say about man's heart and the devices within it?

Proverbs 19:21 states, "There are many devices in a man's heart; nevertheless, the counsel of the Lord that shall stand." This verse emphasizes the contrast between the schemes and plans that arise from the human heart, which are often rooted in deceit and folly, and the immutable purpose of God that is revealed in His Word. The heart, representing a person's will and intellect, tends to devise cunning plans that may lead away from God’s will. Each individual, by nature, is fallen and prone to devise ways that are not in alignment with divine counsel. However, it is God's Word, which provides the true and everlasting counsel that should guide our lives, worship, and salvation. This highlights the need for reliance on God's direction over any of our own deceitful inclinations.