All the activities of the church are to accomplish the common goal of discipleship. This is the case whether we are evangelizing the lost in order to make disciples in the salvific sense or we are engaged in the work of sanctification of the body of Christ. While the church engages in discipleship outside its walls, our gatherings ought to be defined by discipleship. Among the things prescribed by Scripture that we do when we meet, our singing is no insignificant thing!
So, how does singing help make disciples? I can see at least 4 ways…
First of all, doctrine builds us up regardless of the form it takes. Assuming the church is in fact engaged in “doctrinal singing” (that is we are singing songs deeply rooted in the Truth of God’s Word), our songs are being used to reiterate those truths that are otherwise personally studied and publicly preached. This is why our singing is vital to the spiritual health of the church. Singing echoes Scripture's timeless truths, building up our spirits and uniting us as the body of Christ. As Paul writes in Colossians 3:16“Let the word of Christ dwell in you richly, teaching and admonishing one another in all wisdom, singing psalms and hymns and spiritual songs...” The Word of God must dwell in our hearts and must thereby permeate every facet of both our personal and corporate worship. When this is the case, the church is spurred on, our faith is strengthened, our knowledge is increased, and our love is deepened.
Along these same lines, music is particularly effective at cementing the truths of scripture into our minds. It is memorable and has a catechizing effect. Every one of us can testify to having a tune incessantly stuck in our head, or even subconsciously singing a song we heard recently. This is why 25 years later, I can still remember every song from the musical I performed in 2nd grade.  In the same way, when we set our minds and hearts to sing together of the greatness of our God, we implant truths that are to be remembered. Cadence, melody, and lyric have a way of penetrating the mind and heart, implanting themselves there, and causing us to continually recall them days, years, even decades later. Martin Luther said, “Next to the Word of God, the noble art of music is the greatest treasure in the world.” I tend to agree in that by music, the word of God can be more easily remembered, recalled, and retold. 
Thirdly, it is encouraging to sing with and to each other. Again, Colossians 3:16 is helpful here. “…teaching and admonishing one another in all wisdom, singing psalms and hymns and spiritual songs…” For this reason, our worship is to  be congregational. As the body of Christ, we sing Truth together, in one accord to the Lord. This aspect of congregational worship has been all-but-lost in much of the modern era, where we have exchanged the sounds of the congregational body for the voice of one or two. For example, when we dim the room and raise the volume so that we cannot hear each another sing, we have lost something important. Worship through singing, while unequivocally directed at and for the exaltation of Christ, carries also the secondary benefit of reminding us of our eternal home, where we will join with those already in the presence of the Lamb who was slain, singing together, “Holy Holy Holy” (Rev. 4:8)!
Lastly, our worship through song is an avenue by which we experience the fullness of proper emotion. Many believers have the tendency to run to one of two extremes in regard to emotion. Either they seek emotional experiences, viewing emotion as an indicator of spiritual depth, or they see emotion as dangerous, and therefore something to be avoided. However, emotion can be extremely beneficial if we treat it as it is to be treated, as the result and not the object of our worship. The biblical Truth of who God is and all He has done for us in Christ should produce in us everything from gladness, joy, gratitude, love, peace, etc. Once again, Colossians 3:16 guides us. We are to sing “with thankfulness in our hearts to God.”  John Piper sums it up well: “Truth without emotion produces dead orthodoxy and a church full (or half-full) of artificial admirers. On the other hand, emotion without truth produces empty frenzy and cultivates shallow people who refuse the discipline of rigorous thought. But true worship comes from people who are deeply emotional and who love deep and sound doctrine. Strong affections for God rooted in truth are the bone and marrow of biblical worship.”
Brothers and sisters, let us sing to the Lord the truths so clearly displayed in His Word. Let us sing them with passion and conviction, let us sing them to God and very much along side one another. And as we sing, may our hearts be stirred with proper affection and gratitude to our Lord and Savior, Jesus Christ.

Ryan Bailey