When and where are we justified to make money from our worship music? While selling a physical album to cover material and postage costs seems quite proper, I find the issue of downloads to be a grey area. I-tunes and Amazon do not offer the option of giving away your album for free but as the main suppliers it is probably a good idea to be there.
Factors to bear in mind:
Pastors usually get paid.
Church organists (and cleaners) may get paid.
Other church musicians usually do not get paid.
Jesus did it for free!
I have had an opportunity to meet Kim Walker and Phil Whickam on two separate occasions over the past few months. Both had a very genuine love for God and are pioneering some great worship music. Neither of them are seemed to be generateing wealth from their music but the album sales seem to provide a living to continue making great music. In Israel in the old testament Rabbis were supported by others so they could study God's work without distraction. I think we need musicians who create new music to be without distraction.
Two things come to mind:
1) One can receive compensation from their work and still have their priorities where they should be. This is the same for pastors and music directors. And number 2) below informs this.
2) Very very few Christian artists are getting as much as or more than a subsistence level of compensation from their work. I think it's fitting to support what they do if we benefit from it.
There are some christian artists who have done well, but a few got too big and too big in the head and ran off the tracks morally and have lost their witness.
I like Paul Baloche for this reason - his chord sheets and arrangements are up on his website for free to the whole community. And yet, he has written some excellent worship music that you can buy on iTunes or as a CD. But the fact that he has put his music out there for all of us to use seems like a good balance.
As for "Jesus did it for free" - so did Paul. But he indicated it was by choice. Generally, a minister to the Lord's people has a right to expect the community to support him/her. This was started with the Levites in the OT and confirmed by Paul:
" Do I say these things on human authority? Does not the Law say the same?  For it is written in the Law of Moses, “You shall not muzzle an ox when it treads out the grain.” Is it for oxen that God is concerned?  Does he not certainly speak for our sake? It was written for our sake, because the plowman should plow in hope and the thresher thresh in hope of sharing in the crop.  If we have sown spiritual things among you, is it too much if we reap material things from you?  If others share this rightful claim on you, do not we even more?
Nevertheless, we have not made use of this right, but we endure anything rather than put an obstacle in the way of the gospel of Christ."
(1 Corinthians 9:8-12 ESV)
And don't forget that Jesus was supported to some degree by the community of disciples who followed Him.
I agree with Matthew and Stevo -
1 Timothy 5:17 says -- For the Scripture says, “You shall not muzzle an ox while it treads out the grain,” and, “The laborer is worthy of his wages.”
As a musician, if I make my living writing music, I deserve payment. As a pastor, if I make my living preaching and caring for a congregation, I deserve payment.
How much payment you ask? I don't know! I suppose that is up to those making the payment!
So, if, as a songwriter, you are only doing it for the Lord and for His children on a "part-time" basis, no payment is required. This category probably fits most of us. However, if you are spending 40 or more hours a week doing the Lord's work, some sort of support is needed. "The laborer is worthy of his wages.”
God Bless You!
God judges the heart - look at your own heart and what is more important to you? Is it money or is it God's glory? If the priority is money, then walk away from it, as you would be led astray. But if it is the Glory of God then will bless you for your good workmanship.