All of God’s attributes are dependent upon his eternal being. If God has an end, none of his attributes which we recognize as being unlimited can be. What this means to us is that, if God is not eternal, his promises are meaningless; for if he ceases, his covenant ceases.

   If God be eternal, his covenant will be so. It is founded upon the eternity of God; the oath whereby he confirms it, is by his life. Since there is none greater than himself, he swears by himself (Heb. vi. 13), or by his own life, which he engageth together with his eternity for the full performance; so that if he lives forever, the covenant shall not be disannulled; it is an “immutable counsel” (ver. 16, 17). The immutability of his counsel follows the immutability of his nature. Immutability and eternity go hand in hand together. The promise of eternal life is as ancient as God himself in regard of the purpose of the promise, or in regard of the promise made to Christ for us. “Eternal life which God promised before the world began.” (Tit. i. 2): As it hath an ante-eternity, so it hath a post-eternity; therefore the gospel, which is the new covenant published, is termed the “everlasting gospel” (Rev. xiv. 6), which can no more be altered and perish, than God can change and vanish into nothing; he can as little morally deny his truth, as he can naturally desert his life. The covenant is there represented in a green color, to note his perpetual verdure; the rainbow, the emblem of the covenant “about the throne, was like to an emerald” (Rev. iv. 3), a stone of a green color, whereas the natural rainbow hath many colors; this but one, to signify its eternity.

—Stephen Charnock, The Existence and Attributes of God (Baker Books, 2005), 1:297.