What is the purpose of the caveat in Hud (11:108)?

The Qur'an repeatedly says that paradise is unending. For example, in Luqman (31:8-9), it is said > Verily, those who believe and do righteous deeds, for them are Gardens of Delight to abide forever therein. A promise of Allah in truth. Another example is that, in Al-Hijr (15:48), it says > Fatigue will not touch them therein nor shall they be removed from it. However, in Hud (11:108), it is said that > And as for those who are blessed, they will be in paradise, abiding there in for all the time that the heavens and the earth endure, except what wills your Lord: a gift without an end. As quoted, Hud (11:108) does say that paradise is a gift without an end, but I am wondering what is the purpose of the part that says "except what wills your Lord." Is there a generally accepted view on this phrase? The previous verse, Hud (11:107), makes a similar remark about potentially being saved from hell, ending with saying > Verily, your Lord is the doer of what He wants.