One of the things we do at The Journey is that almost all our messages come in the context of series that we do (i.e. a series called "Back From The Dead", or the series we just wrapped up called "I Became a Christian, and All I Got Was This Lousy T-Shirt"). So, why do we do series?
Series serve as markers, as memorials in the lives of Journeyers. When we ask people when they started coming to The Journey, most say something like "oh, we started coming during the EPIC series", or "we came during Desperate Households".
In the book of Joshua, the people were moving into the Promised Land, and Joshua was leading them. God did a miracle and they crossed over the Jordan River on dry ground. Joshua commanded the people to take up some large stones from the river and to set them up on the river bank as a reminder, a memorial, a marker of what God had done. Series are like that for individuals, but they also remind us as a church as to where we've been and what God has done.
That's also why we try to tie "catch phrases" to our series, and why we use certain phrases over and over again. They serve as markers in people's lives of what God is doing. Like "your heritage might not be what you wished it was, but your legacy can be more than you dreamed", or like "God is the blessor, we're the blessed, to be a blessing", or like in our "I Doubt It" series - "don't let a bout with doubt knock you out", or in our "Tattooed" series, where we asked "Who's tattooing you?"
We all have certain phrases, certain markers that we look back on and see as significant moments in our spiritual journey. So, we try to help people with those and then create memorials of those moments (which is why we have the banners from those series' on our walls, and why we give them away when they come down off the walls).