It says it right in the preface.
The mission statement of Insight for Living, the Bible-teaching ministry of Chuck Swindoll, states that we are committed to excellence in communicating the truths of Scripture and the person of Jesus Christ. And while a grace-based ministry such as ours allows for freedom of interpretation and expression in many areas of Christian practice, we believe that the following essential beliefs are absolute and non-negotiable.
That’s great, but non-negotiable for what? For their ministry perhaps, but salvation?
Under Salvation, the clear statement is: “Simply through believing the good news that Christ died for his or her sins and then rose from the dead, a person can be forgiven of all sin, declared righteous by God, reborn into new life, and guaranteed eternal life with God”
Can’t get any clearer than that.