The worst of all mistakes...

There are lots of things that affect our spiritual lives negatively.  Pride.  Anger. Covetousness. Rebellion.  Of all of them, the very worst is not listening, and hardening your heart.
Why? Because you can't recover from it, and you won't survive it.
Here's what happens:
First, you don't want to hear the truth: you won't listen, and that hardens your heart:
"Today, if you will hear his voice, harden not your heart..."
Then, your heart becomes continuously hard...
"The heart of this people (Israel) has become gross, and their ears are dull...,and they've closed their eyes, so they won't see with their eyes, hear with their ears, and understand with their heart..."
In essence, failure to listen becomes a habit, an evil habit, that influences all of life, and we develop a sinful, unbelieving heart--a heart that now doesn't want to listen, just wants to get away from the God who is speaking, and finally "departs from the living God."
At last, we cannot hear, because we would not hear.
And therefore we cannot be converted, and receive the healing power of God, all because we didn't want to hear. Why?
All that God has for us is offered on the condition that we listen to Him.  Failure to listen eventually brings us to the point of not being willing to hear, then not being able to hear, and finally nothing can help us because we have hardened our hearts completely.
This is what happened to the Pharisees in Jesus' day.  They wouldn't listen.  Then they didn't want to listen.  Then they couldn't listen.  At the end, they plotted Jesus' death, even in the face of the greatest of His miracles, the raising of Lazarus from the dead.
John summarizes it when he says, "Though He had done so many miracles, they still didn't believe...so that the saying of Isaiah the prophet might be fulfilled, when he spoke, 'Lord, who has believed our report...'
and,
"Therefore they could not believe, because Isaiah said again, He has blinded their eyes, and hardened their heart..."
Do you want to be like this?  Always unbelieving, rejecting, and finally losing out on the best opportunity God has ever offered mankind.
You don't have to be.
Tell God, "I want to hear from you," and He will speak to you.  Listen for Him, and then listen to Him. Don't think that He will ignore you, because He will never disdain your prayers.Doesn't matter who you are, where you've been, what you've done.  He will listen.