"In Hebrew the word for 'faithfulness' has the same root as the word 'Amen'. So when we say 'Amen' to something, we are saying, 'That is true. It is a faithful saying. In light of this, it is interesting that in Revelation, when the Lord Jesus Christ is being spoken of, he is introduced as 'the Amen, the faithful and true witness' (Rev. 3:14) This is his essence, in other words. Faithfulness is God's nature. Time does not change Him, as it changes us, Nor do moods change God as they change us.
You know how it is with people. At work someone will say, 'How are we going to find the boss today? What sort of weekend will he have had? Has he had a difficult time with his family? If so, is it going to make it difficult for us. I wonder if he will be the same as he was on Friday? One of the problems we have is that we imagine God being like the people we see around us-fluctuating, different, changed by moods, health, stress and provocation. But Psalm 102:27 says, 'You remain the same.' All else may change, but God is constant."