An often missed key to this passage is this:  it is the disciple John who brings this problem to Jesus' attention.  John is the intellectual leader of the disciples, but he is not immune to human passions.
The disciples have just been instructed regarding their debate on "who is the greatest."  That discussion has now settled the issue--within the disciples.  But John, perhaps out of jealousy, asks about those outside the band of disciples.  In so doing, he brings up one of the enduring intellectual problems of the church.
The will of God
It is clear from the Scripture that God's will is to be our command.  There are two aspects of God's will which are pertinent here:

• It is abundantly clear that it is God's will that everyone be saved.  We know that not all will be saved--but that's what God wants.
  
• It is also God's will that his disciples will be one, as Jesus and the Father are one.
  

• Do you see someone, like Apollos, whose knowledge of Christ is incomplete and incorrect?  He is with us.  Therefore we should teach such a person the better way.
  
• Are there those among us who hold differing opinions on various matters?  What did you expect, that Christians would be nothing but zombies?  These we must not only tolerate, but love as brothers and sisters.
  
• And to those in other denominations, we need to reach out.  They worship the risen Savior as we do;  we are one with them.  We should not let the divisions of man triumph over the unity of God.