The Bible teaches that a man becomes what he practices in his thoughts, words and deeds:

[Pr 23:6-7 NAS]:

(v. 6) "Do not eat the bread of a selfish man, Or desire his delicacies:

(v. 7) For as he thinks within himself, so he is. He says to you, 'Eat and drink?'

But his heart is not with you.

"For as he thinks within himself, so he is.." ? A man becomes what he practices - in his thoughts, words and deeds. So even what he dwells on in his mind evolves into the kind of man that he becomes.

[Pr 28:22a]:

"A man with an evil eye hastens after wealth,..."

A man who has an "evil eye" describes a man whose thoughts are evil and who therefore inevitably practices the evil which he thinks about in his mind.

[Ps 141:4]:

" [O Lord, (v. 3)] Do not incline my heart to any evil thing,

To practice deeds of wickedness..."

So out of the mentality - the mind - comes the deeds of a man. Good or evil is first practiced in a man's mind. A man must have thoughts within his mind which then result in his actions; his actions determining the kind of man that he is - and the judgment that he will receive.

Even what a man says determines the kind of man that he is:

[Mt 12:33-37]:

(v. 33) "Make a tree good and its fruit will be good, or make a tree bad and its fruit will be bad, for a tree is recognized by its fruit.

(v. 34) You brood of vipers, [our Lord is speaking to the Pharisees who are trying set Him so they would be justified in killing Him] how can you who are evil say anything good? For out of the overflow of the heart the mouth speaks.

(v. 35) The good man brings good things out of the good stored up in him, [his thoughts would be the only way a man can store up good in himself] and the evil man brings evil things out of the evil stored up in him.

(v. 36) But I tell you that men will have to give account on the day of judgment for every careless word they have spoken.

(v. 37) For by your words you will be acquitted, and by your words you will be condemned."

For a man's words truly reflect the kind of person that he is and that is how a man is judged: by the kind of person that he is. The problem is that all men's minds, believers and unbelievers alike, are contaminated with a sin nature which produces an evil humanistic or human viewpoint - certainly not the divine one which is reflected in God's Word, (cp Ro 3:19, 23; 7:17-23 Ps 5:5). The solution is to saturate one's mind with what God's says in His Word, replacing the human viewpoint with divine viewpoint, thought by thought. This takes an earnest lifetime study and obedience to what the Bible teaches. So the object of a believer is to train his thoughts in accordance with Bible doctrine. That is why a believer is commanded to control his thought life:

[Phil 4:8]:

"Finally, brethren, whatever is true, whatever is honorable, whatever is right, whatever is pure, whatever is lovely, whatever is of good repute, if there is any excellence and if anything worthy of praise, let your mind dwell [think] on these things."