Was this kind of relationship between God and His people seen anywhere else in the Bible?
No. This kind of relationship—believers as members of Christ's body, in Him and He in them—was never seen anywhere else in Scripture. It was not seen between Israel and God, nor between Abraham and Jehovah, nor between Moses and Jehovah. It is the great mystery Paul speaks concerning Christ and the church.
Les teaches that this union is unique to the church, the body of Christ. In Ephesians 5, Paul writes that we are members of His body, flesh, and bones—totally integrated with Christ Himself. We are in Him, and He is in us, a two-way street. Paul calls it a great mystery, a secret God revealed to him. Les points out you never saw this kind of relationship anywhere else in Scripture, not even between Israel and God, Abraham and Jehovah, or Moses and Jehovah. But ours is greater.