'Assuredly' in the Bible

And it came to pass in those days, that the Philistines gathered their armies together for warfare, to fight with Israel. And Achish said unto David, Know thou assuredly, that thou shalt go out with me to battle, thou and thy men.

And David inquired of Jehovah, saying, Shall I pursue after this troop? shall I overtake them? And he said to him, Pursue; for thou shalt assuredly overtake them and shalt certainly recover.