In the 4th chapter of John's first epistle, John implores his audience not to accept every spirit, because there are many false prophets in the world. He didn't leave us to figure out how to do this. There is a test to see when the spirit of God is present in a thing. It is a simple question: Who is Jesus?
False prophets deny that Jesus Christ has come in the flesh. A spirit of God, by contrast, will always confess the incarnation. Now, obviously there's one caveat here: It has to be the Jesus Christ (2 Corinthians 11:4). But if someone confesses Jesus to be the fleshly incarnation of God Himself, that is from God. If anyone denies that, John goes as far as to call them an Antichrist (v3).
John continues: "You are of God, little children, and have overcome them, because He who is in you is greater than he who is in the world. They are of the world. Therefore they speak as of the world, and the world hears them. We are of God. He who knows God hears us; he who is not of God does not hear us. By this we know the spirit of truth and the spirit of error."
Thus the test is complete. If someone is of God, they will confess the incarnation, and when they speak to the world, the world rejects them, whereas it gladly receives those who are not of God.
Tragically, many in the Church today are quick to dismiss various forms of music as "sinful" and "worldly", usually because they personally don't like it. I've even heard Christian rock music described as "Christian sex music", despite never having heard a single reference to sex in any Christian rock song. (Side note: There is one Christian rap song I know that references sex. It's called "No Wed No Bed" by Pettidee, in which the singers describe God's design for sex as being a thing intended only to be enjoyed by a married couple, so hardly the best example of sin in that genre). The truth is, modern Christian songs pass John's test just as easily as old hymns.
The example I am most fond of using is Jesus be Glorified by Skillet. Skillet is frequently attacked for their more veiled songs which, though still intended to have Christian themes, are not so obviously Christian that they would be appropriate for church. But Jesus be Glorified is an obvious exception. This song sounds almost like it was plagiarised from the Bible and put to a rock beat. And of course, it is so powerfully and obviously Christian that unbelievers find it grotesque. In other words, it confesses that Jesus Christ has come in the flesh, and the world really doesn't want to hear it.
Another example I use a little less commonly is Holy Soldier's Stranger. Holy Soldier looks like your average 80s band, the members even having the same ridiculous hair cut you would expect from that era. But Stranger, released in 1985, has a different message than the booze, drugs, and women you expect from a classic rock song. Rather, the song is a not-so-veiled description of Jesus' ministry, even going as far as including the line "But in the end He rose again, His name was Jesus Christ", which would be a career ending line in our modern world.
Pulled from the Deep by Wolves at the Gate does something which I consider to be even more powerful. Towards the end of what is undoubtedly a very powerful song, the band breaks away and cuts to a spoken verse: "God became a man to redeem a sinful humanity, and in becoming a man He lived a perfect life. Then after He went to the cross, on that cross He bore your sin and as bearing your sin the Father in heaven crushed His only begotten Son." The song then continues its emotional description of the grace of God that has truly pulled us from the deep.
These songs are not sinful. They are not devil worship, they are not worldly, they are not intended to glorify sex, violence, or substance abuse, they are extremely powerful testimonies designed to both glorify God and even bring many people to Him, and they have. Countless people have come to faith through these bands, and when God hears them being sung, or even just played with a praise-filled heart, He receives the same pleasing aroma as when the faithful would sacrifice to Him on altars of mud and stone. These songs confess the Lord, they are heard by the faithful, they turn hearts to Christ, they are often rejected by the world. It is astonishing to me that people can look you dead in the eye, and with a straight face call these things "devil worship".
In Colossians 2:16-17, we are told to let no one judge us in food, drink, sabbaths or festivals, because they are a shadow of things to come. When we get to Heaven, we will see just how bland our music really is. What is now your favourite song will be worth less to you than your least favourite when you hear the music in Heaven. Let us therefore not allow ourselves to be divided over how we worship, but let us instead consider who we worship. We worship the Stranger described in Holy Soldier's song, who is certainly no longer a stranger to us. We worship the only begotten Son of the Father, who was crushed by the Father Himself while bearing our sin. Truly, Jesus deserves to be glorified, and I will gouge out my own eyes before I let any Pharisee tell me how that must be done.