That is a great question.  Let’s begin by reading Romans 12:1-2, “I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. And be not conformed to this world: but be ye transformed by THE RENEWING OF YOUR MIND, that ye may prove what is that good, and acceptable, and perfect, will of God.”

How important are the exhortations in these two verses!  To ‘beseech’ means to ask strongly, desire, exhort.  It is a strong word indicating great importance.  The appeal to ‘present your bodies a living sacrifice’ to God is based upon the ‘mercies of God.’  The word ‘mercy’ has already been used ten times in this epistle as the Apostle Paul spoke much of the Lord’s undeserved mercy to us.  Realizing how great we are indebted to the Lord because of His mercy towards us, Paul appeals us to give ourselves totally to Him.  We have a similar exhortation in Romans 6:13, “Neither yield ye your members as instruments of unrighteousness unto sin: but YIELD YOURSELVES TO GOD, as those that are alive from the dead, and your members as instruments of righteousness unto God.”  We might determine to stay busy in the cause of Christ.  We might determine to serve Him in an effective way.  However, in reality, the Lord simply wants us to give ourselves to Him so that He might direct our activities for Him.  To be a true servant of the Lord, we must learn to live our lives according to His will, not ours. 

We read in Matthew 10:24, “The disciple is not above his master, nor the servant above his lord.”  To live a life of true servitude is called our ‘reasonable service.’  This is in contrast to the unreasonable service of going after idols to serve them.  An idol would be anything we place above the Lord and give it a higher place than we do the Lord.  We are exhorted by Peter in 1 Peter 2:5, “Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ.”

We cannot truly give ourselves completely to the Lord if we follow the ways and morals of the world, therefore we are told not to be conformed to this world. The Lord requires that we live, “As obedient children, not fashioning yourselves according to the former lusts in your ignorance.” (1 Peter 1:14).  The Lord requires us to live a life in separation from the world and all its evil deeds and thoughts.  We are told in 2 Corinthians 6:17-18, “Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, And will be a Father unto you, and ye shall be my sons and daughters, saith the Lord Almighty.”

While the Lord does not want us to be CONFORMED, He does want us to ‘be TRANSFORMED by the renewing of your mind.’  That can only happen when the Holy Spirit changes our thinking through consistent study and meditation in His Word.  When we become occupied with the Lord by learning and growing in the Bible, the Lord will change our desires and thoughts.  As we continue in the Word, He will cause us to be more like Himself and we will begin to desire His will for our lives.  Indeed, that will cause our minds to be renewed and we will be transformed!  The Greek word for ‘transformed’ is “metamorphóō.”  It is the same word from which we get the English word ‘metamorphosis.’  That indicates that we leave the old ways behind and live a life that compliments and honors the Lord.

The renewed mind is one which is filled and controlled by the Word of God.  The renewed mind can prove (discern) “what is that good, and acceptable, and perfect, will of God.”  We can serve Him properly because we know Him well and have a greater understanding of what He is like.  (CC)  (508.2)