From what I can discern, a mediated summons is an invitation given on behalf of another. It is a call to someone but given by someone else; someone other than the one who is being “pointed to”. We see a mediated summons a few times in John’s Gospel right in the beginning in chapter one.
For example, John the Baptist leads Andrew and an unnamed disciple to Jesus in John 1:35-39. We also see this motif (distinctive to John’s literary style) when Andrew gives a mediated summons to Peter in John 1:40-42. Philip then does the same thing to Nathanel in John 1:43-51.
As one can see, this device is especially suited for the call stories of the gospels.
The relevance is that we, the church, are to do this to those around us. We are the mediators summoning others to Jesus – at least we should be. I hold that the way this happens is through the preaching of the gospel. Verbal proclamation is absolutely essential. This doesn’t mean it’s easy or that God does not use all types of means to draw people to himself – He is in control. Yet the apostolic model (following after Jesus) is to speak God’s truth. Still, I believe that outreach must include love and when possible, real relationship.
The world is filled with those who are just like we were – not found in Christ. Since it is by God’s grace that we are saved, we cannot look down on non-believers or dare think we are superior to them in any way. And even though we war against Satan, we should not think of the unsaved as targets or enemies. They can be our friends and we must show them the love of Christ as we call them to him. The gospel proclaimed is the essential way. However, other means can be ancillary, such as art, literature, music and the like.