Blended worship has as its goal the joining together of the people of God in all their diversity, under one roof and in one service, to glorify God through the offering up of corporate praise. The term "blended" speaks of the artful weaving together of varying musical styles and other elements into a seamless tapestry which honors the Lord without alienating any particular group.
The strongest argument which can be marshalled in favor of blended worship (as opposed to offering different types of services, such as "traditional" and "contemporary," or only one specialized type) is a biblical and theological one. It relates to the very nature of the church: worship should rightly be blended because the body of Christ itself is blended (see I Corinthians 12). By definition the church gathers into one living organism people from all different backgrounds and walks of life; in fact, unity within the kind of diversity seen in the church is in itself a testimony to the divine nature of the institution (Galatians 3:28; Ephesians 4:1-6) -- for, while by nature "birds of a feather flock together," Christ's body invariably includes an unusual combination of quite disparate individuals, who have in common only their faith in and love for Christ.
But that is the whole point! In order for corporate worship (unarguably the most important thing the church does together) to accurately reflect the nature and the unity of the body, it must include the people of God in all of their diversity, unified in the worship by the common focus of that worship: the Lord Jesus Christ, the King of glory.
That Christ-centered focus is the key which allows us to transcend petty, man-centered squabbles over musical taste and preference. For if we are united in our commitment to the glorification of our Lord through our worship, we will be blessedly distracted from lesser things which might divide us. And it is in our corporate worship of all places, as the most purely God-directed activity of the church, that our unity should be most in evidence. It is a scandal that worship has too often engendered the most divisiveness among God's people (in what one writer has referred to as "worship wars")!
In fact, for true blended worship to really work, all of God's people must be willing to make concessions relative to their own personal preferences - no one will get just the kind of music he or she likes all the time, but that becomes an acceptable sacrifice in light of the common good. (But it is important that all are called upon to make stylistic concessions, not just one group.) And even beyond the worth of harmonious corporate worship, the process of making such concessions is in itself a spiritual exercise of inestimable value. It is well-pleasing to the Lord when we prefer one another in such a way (Romans 12:10; Philippians 2:3) and "consider one another as more important than ourselves."
So may we focus in our worship on the One who alone is worthy of our worship, and in so doing bring to expression the oneness which all we who have trusted in Christ genuinely share. May we seek to please the Lord with our worship, bringing our humble gifts of praise and esteeming as well as the gifts which others bring, to the end that He might be honored not only by our outward expressions but also by the attitudes of hearts (which are much more important to Him anyway!). May our worship reflect the unity within diversity which is the beauty of Christ's body, blending "psalms, hymns, and spiritual songs" (Ephesians 5:19) in a harmonious symphony of praise.