Theists: What do you mean when you say that God is 'perfect'?

[Angrboda]

In a recent conversation with a theist, I asked what makes something 'perfect'. Their response was that something is perfect if it is "maximally ideal for its intended purpose." I see this as basically correct. What makes something a perfect coffee maker would make that same thing a lousy microwave oven, and vice versa. It seems that to be perfect, a thing must be in some relation to a purpose or an end or a goal such that it maximally fulfills that end. But here we come upon a problem, because God doesn't have such. There is no end or purpose or goal which is defined for God. It would seem at first glance then, that the word simply doesn't apply to God. If I had a nondescript object on my kitchen counter which had no purpose, what would it mean for me to say that it is 'perfect'? The best that could be said is that I'm using the word 'perfect' as a superlative, like saying that something is 'super' or 'awesome'. Yet theists continually assert that their God is 'perfect' and seem to want to mean something more by it than just a superlative, but what do they mean? Some take the lazy way out and claim that God's perfectness applies to "everything" -- God has all possibilities in the maximal degree, but this is clearly incoherent. An object which contained all perfections (whatever that means) would include perfect justice and perfect mercy. Since justice consists in giving people what they deserve, and mercy consists in giving people less than they deserve, the two can't be perfectly fulfilled at the same time. So the 'everything' answer is ruled out.

So what do you mean when you say that God is 'perfect'?