“Yahweh is the true God; he is the God of the living and the eternal King. The earth shakes from his wrath and the nations cannot bear his curse.”
There are many adjectives that are applied to God: mighty, glorious, faithful, etc… but perhaps two of the most common and most important are that of true and eternal. Essentially, what these adjectives communicate is that God is the one true God — there is no other and all others who seek to present themselves as God are false and only lead mankind astray and into eternal condemnation. In addition, this is the way it has always been and will always be, for not only is God true, but he is eternal and not bound by the constraints of time as are we. To God there is no before and no after; he never changes, learns new information, or weakens. He simply is. And thus, if we are going to stand in this life and in the next, we must stand upon the foundation He has laid.
And thus, as Question 25 of Heidelberg comes to a close, it affirms both of these adjectives in the context of who our Triune God is…and who he will always be. So note, not only is this statement being made in the broad sense of God, but in the catechism, it is being made of the Triune God. Numerous heresies have arisen around the nature of the Trinity (some say that God did not become Triune until the birth of Jesus, others say that he is divisible, others say that God was just taking different forms), yet the catechism affirms that God is Triune, he has always been Triune, will always be Triune, and that this is the only true way to understand who God is.
Why is this important for the individual Christian in his day to day life? First, because the things that he has been taught (assuming they were taught correctly) are not going to change. God is the same yesterday, today, and eternally. This, my friends, is the true faith in service of the true God. If one would be saved, let him believe on these things.