'Assuredly' in the Bible

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