If it is not impossible for Allah ﷻ to be attributed with some quality, then it is necessary for Him to be attributed with this quality. This is because the existence of said quality would either be:
Allah cannot be attributed with a quality whose existence is possible, as this would necessitate this quality’s emergence. And a beginningless being cannot be attributed with emergent qualities, as that entails change on His part, while a beginningless being is necessarily changeless.
This means that the existence of any quality that is proposed for Allah ﷻ is either impossible, or necessary. Such that if the existence of said quality were not impossible, then its existence would be necessary. And since the non-existence of a necessary quality is impossible, this means that Allah ﷻ must be attribute with it.
In conclusion: not only is the existence of all of God’s qualities necessary, but it is also the case that He is attributed with all qualities whose existence is necessary.
 If a quality were emergent, then this would mean that Allah ﷻ transitioned from a state of lacking said quality, to a state of being attributed with said quality. This is a change.
 Whatever has the potential to change is inseparable from accidents. And that which is inseparable from accidents is emergent. Therefore, whatever has the potential to change is emergent. And since God is not emergent, then God is necessarily immutable. More on this here.