There are many church websites that state that the worship service is a contemporary style or a blended style. There is an ever present danger with becoming slack in the practices of worship towards the Almighty God. God demands to be worshipped in a very distinct and holy way. Several dangers are discussed here.
The first reason that leniency in corporate worship is an ever present danger is because it is very divisive.

1 Corinthians 1:10 “Now I beseech you, brethren, by the name of our Lord Jesus Christ, that ye all speak the same thing, and that there be no divisions among you; but that ye be perfectly joined together in the same mind and in the same judgment.”

The Lord commands believers to speak the same thing, but also to have the same mind. Multiple styles of music in a worship service do not encourage unity. In fact, because of the differences in traditional hymns and contemporary songs, some churches have been conducting multiple services. One service will be traditional so that those who grew up singing hymns will be comfortable and the other services will be contemporary for those who are tired of the old hymns and need something new and exciting, or grew up listening to rock and roll. Having multiple church services, in order to please different preferences, is not biblical.

Ephesians 4:3 “Endeavoring to keep the unity of the Spirit in the bond of peace.”
Ephesians 4:13 “Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ:”

In the verses above, unity is the prevalent theme and to stare away from unity is disregarding these verses, which is otherwise known as sin. Some might not even realize that music divides the church, but the Bible promotes unity among believers and this is one area where Satan has gained control.
Along with the church services being divided up and because the church is divided into traditional and contemporary, the younger men and women in the church are then separated from the older men and women in the church. It is God’s plan for the older men and women to teach the younger men and women the wisdom and biblical pattern of good works so that God might be glorified. When there is division in the church, how can this be followed? Spiritually mature, older men have wisdom and discernment of how to do things for the glory of God, but may lack the physical energy to actually conduct those ministries and the opposite is true. Young men have the energy to conduct all the different ministries in the church, but might lack the wisdom and discernment of how to honor God. Separating the church worship service into multiple groups is not wise and does not honor God.

A third reason that leniency in worship music is an ever present danger is the intent to have a traditional and contemporary service was to please men. According to the Bible, there is only one way to approach God, with reverence and godly fear (Hebrews 12:28) which does not say anything in regards to using different methods for conducting a worship service and using different styles of music. Saying and thinking that using different methods of worship is glorifying to God is unbiblical.
Everyone has a different preference in this area, but God has revealed many ways that was needed to for the high priest to approach a holy and living God. In the book of Leviticus, the high priest was to wear very specific clothing before approaching the Almighty God. The high priest was to only enter into the holy of holies on the Day of Atonement; each sacrifice had its own rules. Approaching the Almighty God in any other way other than what God says would result in catastrophe. Today’s contemporary Christian music trend has been proving how selfish the flesh is for a long time.

A fourth reason that leniency in corporate worship is an ever present danger is that the attitude or mindset of this trend permeates the atmosphere of a church service. When worldly music is brought into the church service, there is a sense of irreverence and carelessness that comes along with it. We can see this simply by reading the lyrics of a traditional hymn and comparing them with the lyrics of a song from a contemporary Christian music artist. There are great hymns of the faith that are filled with sound, doctrine from God’s Word, conveying the glorious truth of Hiss Word, reverent, boastful in Christ alone, and giving God glory, honor, and praise. When reading the lyrics to some popular contemporary Christian music songs, it’s plain to see the difference in poetic beauty and the sense of reverence towards an Almighty, Holy God. Many of the great hymns of the faith are filled with God’s character and those hymns are very sadly being forgotten. Today’s contemporary worship music, some of which contain very confusing doctrine and some contain almost no truth about the Lord are becoming more and more popular in churches around the country.
40 or 50 years ago, there was an obvious distinction between contemporary Christian music and godly, biblical worship music, because there was little to no contemporary Christian music. As contemporary Christian music became more popular, the attitude and reverence towards our Lord and Savior had diminished and today reverence to the Almighty, Creator of heaven and earth is miniscule when compared to the reverence found in those great and doctrinally sound hymns of the faith. This is certainly something that needs to be reconciled and compared to what the Bible says, but of course God warns in 2 Timothy 4:3 that the time will come when sound doctrine is not endured. Replacing the great hymns of the faith, which are filled with the character of God and sound doctrine from the Bible, with contemporary songs that diminish that character is not only foolishness, but is irreverent to an Almighty God, the God who created this vast universe and everything in it.