Ezekiel 36:26
"A new heart also will I give you,
and a new spirit will I put within you:
and I will take away the stony heart out of your flesh,
and I will give you an heart of flesh."
Now, this sounds a little harsh, but if you look at the foot note for "stony heart" it has the word conversion. That when we are willing to go through the "spiritual surgery" of getting a new heart, we can become more converted. When we except God's will over ours, we ourselves can run faster, learn quicker, be better examples of our Lord and savior.
Ultimately we are suppose to become like the Savior, but we cannot do it on our own and with our old hearts. We have to be willing to go through the pain and grow to become strong. Because we know the pain is only for a small moment, we endure it and allow the 'new' heart to take its place and grow strong within us.
Trials, struggles, and hard times are all for our benefit. For God would not allow something to happen to us that was not for our benefit. He loves us with infinite love and wants us to be able to overcome the natural man and return to the presence of God and we can only do that if we allow the master surgeon to put a new heart inside of us.