The Epistle reading for this day (1928 Prayer Book) is from Galatians 3, and Paul's comments there about our being the children of Abraham. You can view my sermon on the text here - the sermon starts at about 33 minutes into the video.
Mostly stuff on Christianity by an Anglican priest who reads a lot of C. S. Lewis. Please note: all my posts about Lewis' book How To Pray are on the cslewis.org site, under Social Media/blog.