This is the way that the Living God—Father, Son, and Holy Spirit—is addressed.
We just read Nehemiah together as a church, and you might remember that bit where the Israelites confess their sins in chapter 9, and they are led by the Levites in worship, and are told to stand up and praise the Lord their God, and—again—the Levites remind the people that he is ‘from everlasting to everlasting’.
It’s the way that David speaks in the Psalms as well. He often closes psalms by saying those words. Psalm 41 is a good example: “Praise be to the Lord, the God of Israel, from everlasting to everlasting. Amen and Amen.”
And the same in Psalm 103, where David compares the life of God to the life of us mortals and concludes that we are like grass (we’re here today and gone tomorrow and we’re forgotten), but on the other hand, the Lord’s love is from—there it is again—everlasting to everlasting.
You’re starting to see, I hope, how important this phrase is.
Moses speaks that way too in another Psalm. He says of the Living God that “before the mountains were born or he brought forth the whole world, from everlasting to everlasting, he is God.”
Consider the attitude that you must have in terms of an inevitable humility, which must come in the light of the doctrine of the eternality of God, as well as the the work of service which is prayer, which we must all involve ourselves with (especially public-prayer).