The question (said to be in the mouth of an atheist) lacks heart.
We love him (and thus only do we serve him) because he first loved us. [1 John 4:19.]
The question is, in reality, a refusal to serve God on the grounds that he (supposedly) does not 'need' service. But that is a servile attitude, not the response of a freeborn son, who loves the Father. Parables abound which demonstrate these opposite attitudes.
Since a Protestant response is invited, I am quoting Martin Luther.
Extract from 'The Great Fire of the Love of God for us'
Taken from Martin Luther, “A Brief Instruction on What to Look for and Expect in the Gospels (1521),” in Luther’s Works, Vol. 35: Word and Sacrament I, ed. Jaroslav Jan Pelikan, Hilton C. Oswald, and Helmut T. Lehmann, vol. 35 (Philadelphia: Fortress Press, 1999), 119-120.
“The chief article and foundation of the gospel is that before you take Christ as an example, you accept and recognize Him as a gift, as a present that God has given you and that is your own.
This means that when you see or hear of Christ doing or suffering something, you do not doubt that Christ Himself, with His deeds and suffering, belongs to you. On this you may depend as surely as if you had done it yourself; indeed as if you were Christ Himself.
See, this is what it means to have a proper grasp of the gospel, that is, of the overwhelming goodness of God, which neither prophet, nor apostle, nor angel was ever able fully to express, and which no heart could adequately fathom or marvel at.
This is the great fire of the love of God for us, whereby the heart and conscience become happy, secure, and content. This is what preaching the Christian faith means.
This is why such preaching is called gospel, which in German means a joyful, good, and comforting ‘message’; and this is why the apostles are called the ‘twelve messengers.’
Concerning this Isaiah 9:6 says, ‘To us a child is born, to us a son is given.’ If He is given to us, then He must be ours; and so we must also receive him as belonging to us.
And Romans 8:32, ‘How should God not give us all things with His Son?’ See, when you lay hold of Christ as a gift which is given you for your very own and have no doubt about it, you are a Christian.
Faith redeems you from sin, death, and hell and enables you to overcome all things. O no one can speak enough about this! It is a pity that this kind of preaching has been silenced in the world.
Now when you have Christ as the foundation and chief blessing of your salvation, then the other part follows: that you take Him as your example, giving yourself in service to your neighbor just as you see that Christ has given Himself for you.
See, there faith and love move forward, God’s commandment is fulfilled, and a person is happy and fearless to do and to suffer all things. Therefore make note of this, that Christ as a gift nourishes your faith and makes you a Christian. But Christ as an example exercises your works.
These do not make you a Christian. Actually they come forth from you because you have already been made a Christian. As widely as a gift differs from an example, so widely does faith differ from works, for faith possesses nothing of its own, only the deeds and life of Christ.
Works have something of your own in them, yet they should not belong to you but to your neighbor. So you see that the gospel is really not a book of laws and commandments which requires deeds of us, but a book of divine promises in which God promises, offers, and gives us all His possessions and benefits in Christ.”