If a person has a hard heart, they won't believe God’s love. Believing God's love puts them in a position of vulnerability and humility, which scares them.
They also won't receive God’s word because it can't penetrate through a hard heart. Or if it does, the Word won't go very deep!
God's word must be able to penetrate the heart and grow in order to produce the fruit of the Spirit: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, and self-control (see Galatians 5:22-23).
Here is another sobering thought: A person can even try to minister to others from a hard heart! But love won't motivate their service. They will serve out of legalism, duty, obligation, and drudgery. It is obvious they do not find joy in their service either.
The Lord gave me this Word on this subject:
"Unless you allow the Lord to heal your heart, you will never grow past the place of your wounding."
The only thing I know that is strong enough to soften a hard heart is the blood of Jesus. In the following article are some truths about Jesus that can help soften the hard heart – if the person will believe.
I also included my prayer for a person suffering from a hard heart in the article.