'Certainly' in the Bible

He went on to say, "In solemn truth I tell you that some of those who are standing here will certainly not taste death till they have seen the Kingdom of God already come in power."

and whoever gives you a cup of water to drink because you belong to Christ, I solemnly tell you that he will certainly not lose his reward.

I tell you in solemn truth that the present generation will certainly not pass away without all these things having first taken place.