Is God able to do anything or is He limited? Abraham is 99 years old and finally has come to the place where he no longer believes he can become a father naturally and God shows up with a promise and a covenant. Jesus speaks of His persecution, passion and death and Peter takes Him aside to rebuke the one he had just confessed was Messiah because that makes no sense, Messiah won't die. Faith isn't a once for all thing, it is always being tested by God to take us higher in Him. 

Psalm 22:22-30

Genesis 17:1-16

Romans 4:13-25

Mark 8:31-38