Beware of the inclinations toward hardness when your heart begins to grow callous, such as:
1 When you no longer sense God's withdrawal, experiencing a suspension of His grace, comfort, and the leading of His Spirit, and your soul becomes dull. It is disheartening not to be aware of the Spirit's movements—when the bridegroom is taken away, as Matthew 9:15 warns, "How can the guests of the bridegroom mourn while he is with them? The time will come when the bridegroom will be taken from them; then they will fast." Grace requires continual vigilance and attentiveness to God's dealings. Felt desertions are grievous, but those that go unfelt are even more perilous. It is an indication of some degree of grace not to be at peace without God.

2 When you scorn rebuke and not only commit sin but defend it boldly and obstinately, persisting in your transgressions. Jeremiah 6:10 laments, "To whom can I speak and give warning? Who will listen to me? Their ears are closed so they cannot hear. The word of the LORD is offensive to them; they find no pleasure in it." Such people are unteachable and intractable; they perceive reproof as mere slander. In this, the devil achieves two victories: through the scorn and opposition directed at the reprover and through the hardening of the heart in the reproved sinner, who becomes angry not at their sin, but at the reproof itself.

3 When the effectiveness of ordinances wanes. You attend church services and receive no benefit from them; you have access to many means, yet see no fruit. Isaiah 6:9-10 states, "He said, 'Go and tell this people: "Be ever hearing, but never understanding; be ever seeing, but never perceiving." Make the heart of this people calloused; make their ears dull and close their eyes. Otherwise they might see with their eyes, hear with their ears, understand with their hearts, and turn and be healed.'" The Word is powerful, but if it does not soften, it hardens.

4 When your worldly comforts become a snare. Malachi 2:2 warns, "If you do not listen, and if you do not resolve to honor my name," says the LORD Almighty, "I will send a curse on you, and I will curse your blessings. Yes, I have already cursed them, because you have not resolved to honor me." Your table becomes a snare, your food turns into poison, your wealth becomes golden shackles that bind your heart to the world, and your honors swell your ego. Instead of seeing comforts as God's mercies and blessings and praising Him for them, dedicating yourself and your resources to His service, you fail to do so.

5 When corrections yield no fruit: Jeremiah 5:3 states, "You struck them, but they felt no pain; you crushed them, but they refused correction. They made their faces harder than stone and refused to repent." God keeps a record of every dispensation; afflictions are noted alongside blessings. Christians should make their greatest progress in Christianity under the weight of the cross.

6 When we are lazy and reluctant to invite Christ into our hearts. With our hearts filled with worldly comforts, we keep Him at the door, knocking, and refuse to let Him in. Revelation 3:20 says, "Here I am! I stand at the door and knock. If anyone hears my voice and opens the door, I will come in and eat with that person, and they with me." Similarly, Song of Solomon 5:3 declares, "I have taken off my robe—must I put it on again? I have washed my feet—must I soil them again?" This laziness and spiritual complacency are the causes and beginnings of hardened hearts.

7 When trivial and insignificant temptations overcome our sense of duty—when we are willing to transgress for a piece of bread or a handful of barley, when we sell our integrity for a pair of shoes. When we become like stones towards God's counsel, but like wax towards everything else.

8 When the heart becomes empty and superficial, for a frivolous heart will become a hardened heart. Alternatively, God may abandon individuals to a reprobate mind and a lack of judgment. These are the warning signs and precursors of a hardened heart that we must be wary of and guard against.

~ Thomas Manton ~The Hardening of the Heart