Just Isaac: Inspired by the story of Sarah and Abraham trying to rush the child of promise Isaac by having Abraham sleep with Hagar. The song is saying we should desire "Just Isaac"---the promise of God and His faithful provision of that promise. We shoudl wait on God's perfect timing of His promise instead of forcing the promise to come to pass.
Surrender: This ties with "All I Need Is Love" as being my all-time favorite song on the album. It talks about how we like to fight the battle ourselves, and how we should try something "old and new" like surrender---surrender everything to God no matter where things may fall.