God's promise as in His holy books that He is the one has desended the core of religion (holy book) and He will protect it.
This can be illustrated in many ways. Few of them are as follows:
None will be able to destroy it;
None will be able to twist it's truth;
None will be able to change or replace it.
The following picture is a miraculous proof:
Recently the house of a poor guy is burnt into ashes by accident (feel sorry for that) but the writings of the holy book inside the house as you can see remain intact.
Its nothing but an evidence that "Promise of God always happen".