In utilitarianism the unit of measurement for benefit is the overall happiness of the majority. If an action or an idea makes the majority happy, then it becomes the moral standard of the community. The problem with this philosophy from a Christian perspective is that it assumes that human beings are inherently good and that this morality of the majority will thus be good.
However, the Bible says, “The heart is deceitful above all things, and desperately wicked: who can know it?” (Jeremiah 17:9). When the majority happiness creates moral standards this wickedness quickly comes to light. Some of the greatest atrocities in the world continue to be committed in the name of the benefits to the majority: genocide, slavery, apartheid, etc. And for a time these things do make the majority happy.
As Christians we do not set our standards according to a majority rule rather we set them according to God’s rule.
Sometimes we imagine that God just wants us to be happy and that His rule will make us happy, which means utilitarianism in some ways would make sense for Christians. However the Bible doesn’t teach that God wants us to be happy. He wants us to be joyful. There is a difference.
It's a lot like the difference between lust and love. Lust is a fleeting desire/emotion in the body that if we choose to act on it can lead to fornication and adultery, but it will vanish just as quickly as it came if it’s resisted or acted on. On the contrary, love is a choice that we make, which is eternal (1 Corinthians 13), as is all the fruit of the Spirit (Galatians 5:22-26). With the Spirit we are empowered to choose these things.
Accordingly, desiring to be happy is a fleeting emotion that can lead to covetousness, murder, and theft, but will vanish just as quickly as lust if it’s resisted or acted on. Joy is an eternal choice. What does it mean to choose joy?
“As the Father hath loved me, so have I loved you: continue ye in my love. If ye keep my commandments, ye shall abide in my love; even as I have kept my Father's commandments, and abide in his love. These things have I spoken unto you, that my joy might remain in you, and [that] your joy might be full. This is my commandment, that ye love one another, as I have loved you.” (John 15:9-12)
In this you greatly rejoice, even though now for a little while, if necessary, you have been distressed by various trials, so that the proof of your faith, being more precious than gold which is perishable, even though tested by fire, may be found to result in praise and glory and honor at the revelation of Jesus Christ; and though you have not seen Him, you love Him, and though you do not see Him now, but believe in Him, you greatly rejoice with joy inexpressible and full of glory, obtaining as the outcome of your faith the salvation of your souls. (1 Peter 1:6-9)
First we must recognize that as a fruit of the Spirit, His joy is our joy. “The joy of the Lord is your strength” (Nehemiah 8:10). Choosing joy is living in Christ, being obedient to Him, and the hope He has given us in the salvation of our souls.
No matter what circumstance may come, whether it be suffering or pleasure, when we choose God's joy, it can never be taken away.