Mind is the element of a person that enables them to be aware of the world and their experience, to think and feel the faculty of consciousness and thought.
Mind is someone ability to think and reason: the intellect. Synonyms: Power of thought, mentality, perception, brain power and reasoning
Why must someone renew his/her mind?
(1). The mind is the battle ground. This is where all the battles of life are fought and won. The devil’s object of attack is the mind so also the word of God can only gained entrance into you via the mind. That is why the scripture says,
Proverbs 4:23 KJV
Keep thy heart with all diligence; for out of it are the issues of life.
(2). Ever since the fell of Lucifer, men thinking pattern have been evil continuously.
Genesis 6:5 KJV
And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
This is why you must deprogram yourself from this negative pattern into the positive pattern. Watch out for what you allow to stay on your mind.
In the realm of the spirit, any thought that you allows to hold grip on you is regarded accomplished.
Your mind can either make you or break you.
(3). God thinks and He thinks positively
Jeremiah 29:11 KJV
For I know the thoughts that I think toward you, saith the Lord , thoughts of peace, and not of evil, to give you an expected end.
3 John 1:2 KJV
Beloved, I wish above all things that thou mayest prosper and be in health, even as thy soul prospereth.
Understand this: the law of the universe demands that every natural force duplicate itself into its offspring.
During creation, God subjected Himself to the same principle.
that creepeth upon the earth.  So God created man in his own image, in the image of God created he him; male and female created he them.
The son of a goat is a goat; a cow can’t give birth to a dog. Likewise in living plant, a mango tree can’t produce a cashew fruit.
It follows that the sons and daughters of God are gods.
Psalm 82:6 KJV
I have said, Ye are gods; and all of you are children of the most High.
If your father thinks and He thinks positively; you have no choice than to think positively.
This is different from the positive thinking of psychology. It is drawing life from the fountain of revealed truth.