Both Francis and Edith Schaeffer believed passionately that all human persons are made in the image of God, and thus have a glory inherent in who they are. This conviction impacted everything they taught, including what they taught about how we are to communicate the gospel to people who are not-yet believers in Jesus. Even more clearly, this conviction of the dignity of all persons impacted the way they treated people, both believers and unbelievers, and it shaped very deeply the manner in which they shared the gospel of Christ with people.
You can read the article Jerram mentions in the lecture, A Review of A Review by Francis Schaeffer.
Also, here are links to more resources from Jerram on the topic of evangelism and the work of Francis and Edith Schaeffer.
Books by Jerram
Learning Evangelism From Jesus
Reflecting on Francis and Edith Schaeffer's Teaching and Practice of Evangelism