I wilt give you the sure mercies of David. (Acts 13:34)
 
Nothing of man is sure; but everything of God is so. Especially are covenant mercies sure mercies, even as David said “an everlasting covenant, ordered in all things and sure.”
 
We are sure that the Loci meant His mercy. He did not speak mere wards: there is substance and truth in every one of His promises. His mercies are mercies indeed. Even if a promise seems as if it must drop through by reason of death, yet it never shall, for the good Lord will make good His word.
 
We are sure that the Lord will bestow promised mercies on all His covenanted ones. They shall come in due course to all the chosen of the Lord. They are sure to all the seed, from the least of them unto the greatest of them. We are sure that the Lord will continue His mercies to His own people. He does not give and take.

What He has granted us is the token of much more. That which we have not yet received is as sure as that which has already come; therefore, let us wait before the Lord and be still. There is no justifiable reason for the least doubt. God’s love, and word, and faithfulness are sure. Many things are questionable, but of the Lord we sing —
 
For his mercies shall endure
Ever faithful, ever sure.

Charles Spurgeon