Please consider the verses below which speaks of the Davidic Covenant lasting to the “age” (or “forever”?) as it is compared to the “same” time period into which the “moon” lasts as well:

“My covenant I will not violate,

Nor will I alter the utterance of My lips.

“Once I have sworn by My holiness;

I will not lie to David.

“His descendants shall endure forever

And his throne as the sun before Me.

“It shall be established forever like the moon,

And the witness in the sky is faithful.”

Selah.” (Psalm 89:34 – 37, NASB)

The question is, will the moon last “forever” or to the “age”?

It’s to the “age”, not forever.

It is readily seen as even the Psalms say that the moon will eventually be no more:

“In his days may the righteous flourish, And abundance of peace till the moon is no more.” (Psalm 72:7, NASB)

and so the literal translation is more accurate:

“I profane not My covenant, And that which is going forth from My lips I change not.

Once I have sworn by My holiness, I lie not to David,

His seed is to the age, And his throne [is] as the sun before Me,

As the moon it is established — to the age, And the witness in the sky is stedfast. Selah.” (Psalm 89:34 – 37, YLT)

Meaning:

The Davidic Covenant is a “shadow” to Christ where only Lord Jesus Christ “reigns to the Ages” (Hebrews 2:8, where Reigning lasts only as long as enemies exist which will be subject to Him eventually, hence “not” forever, 1 Corinthians 15:24 – 28 till God becomes “All in All”) & only after that, “His Kingdom Will know no end” as ‘it is written’ (truths which are only seen when more accurately translated) :

“and He will be King over the House of Jacob for the Ages, and of His Kingdom there will be no end.” – Archangel Gabriel regarding Lord Jesus Christ (Luke 1:33, Weymouth New Testament)

Reign (Verb) and Kingdom (Noun) in Greek share the common root Greek Word.