The very nature of the Gospel requires that it be talked about. People can always live a good, moral, just life, performing excellent works of kindness, charity, healing and forgiveness. These actions are important, and walking your talk is definitely needed to help people understand you're sincere in your beliefs, but you first have to have a talk you're walking. For people to understand your motivation is to live a Christian life, a "Christ-like" life, words are absolutely necessary.
Another author, Ray Comfort (written over 70 books/Christian apologist, http://raycomfortfood.blogspot.com), wrote: "Saying preach the gospel, when necessary use words is like saying, feed the poor, when necessary use food.”
Sharing the stories of the Gospel, the words of Christ - St. Francis did this on a regular, ongoing, life-long basis. And he ensured that his actions matched his words, and expected the same of those who chose to follow in his footsteps.
Adding a quote from our priest, PattiAnn Bennett about St. Francis, taken from The Lessons of St. Francis by John Michael Talbot, p. 192:
"Talk is cheap, but love is costly. When Francis and his friars went out into the world, thy didn't practice a form of hit and run, kamikaze Christianity. They didn't just preach and run. They reached out to people and did what they could do to serve. Thomas of Celano described Francis as "preaching everywhere the kingdom of God, and rendering his whole body a tongue, in order to edify his hearers by his example as well as by his words."I think this makes the whole thing make much more sense.