Ye shall not tempt the LORD your God, as ye tempted him in Massah. Ye shall not tempt the Lord - Ye shall not provoke him by entertaining doubts of his mercy, goodness, providence, and truth.
As ye tempted him in Massah - How did they tempt him in Massah? They said, Is the Lord among us or not? Exodus 17:1-7. After such proofs as they had of his presence and his kindness, this was exceedingly provoking. Doubting God's kindness where there are so many evidences of it, is highly insulting to God Almighty.