At first reading, the chapter of Romans 12 can seem like just a list of things that we should and should not do. "Do not be conformed to this world", "be constant in prayer", "live peaceably with all" and other commands pepper the passage in quick secession. But when you dig deeper, you can see that there is more than a command to do something stated in these sentences. What is really being given is what a changed heart looks like.
"Having gifts that differ according to the grace given to us, let us use them: if prophecy, in proportion to our faith; if service, in our serving; the one who teaches, in his teaching; the one who exhorts, in his exhortation; the one who contributes, in generosity; the one who leads, with zeal; the one who does acts of mercy, with cheerfulness. Let love be genuine. Abhor what is evil; hold fast to what is good. Love one another with brotherly affection. Outdo one another in showing honor. Do not be slothful in zeal, be fervent in spirit, serve the Lord. Rejoice in hope, be patient in tribulation, be constant in prayer. Contribute to the needs of the saints and seek to show hospitality."
If we are, by nature, a teacher or a giver, it is just ingrained in us to teach or give. We were given gifts in our personality that make us who we are. But "the one who does acts of mercy" can do it without cheerfulness. We can feel that it is the only choice we have, but grumble the whole time we do it. But Paul, through the inspiration of Christ, tells us that we MUST have cheerfulness in the act. And the only way we can fullfill that command is for Christ to fill our heart with His joy in those acts.
It isn't enough to hate evil. We have to turn from in and delight in what is good. But our flesh has a heart of stone. We cannot truly delight in the good of the Lord until he has broken our hearts to His will.
Over and over again in the chapter, we are pointed again and again with each command to the second verse; "Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect." We must be open to the conviction of God, so that we may truly delight in his will. We must be given a new heart, starting with accepting Christ as the Lord and Savior of our hearts and repenting of all that grieves Him. Then it will seem joy to serve others and honor Him. And these verses show us what that will look like :).