Cookie A Day
11 For no one can lay any other foundation than what has been laid down. That foundation is Jesus Christ.
-1 Corinthians 3:11 HCSB
As Christians, we must continue building up the person we are ministering to about Christ. We cannot introduce something other than the Scriptures [the foundation] because if we do, we can derail him from coming to salvation through faith in Jesus Christ.
For examples of other foundations: People quoting well known Christian philosophers like CS Lewis, Dallas Willard, John Calvin and the likes.