... the Christian God who has properties such as goodness and love is obviously not necessary since we can easily imagine a God who does not have these properties.
The question of "what happens to the divine nature" when It exercises Its faculty of absolute free will is a labyrinthine one in the history of Christian theology especially (since Trinitarians also have the problem of explaining how the Second Person of the Trinity, with two wills to His name as of the Incarnation, exercised these wills not only in actually perfect harmony but also without the normal human possibility of sin). Here's a quote from a section of an SEP article introducing exactly this topic:
Another frequently-raised objection to the prospect of necessary perfect goodness concerns the relationship between freedom and moral goodness (see, for example, Pike 1969, p. 215; Reichenbach 1982, pp. 133–134). Not all beings are subject to moral assessment; we do not judge rocks to be dutiful because they never violate a moral duty. It is plausibly thought that one of the features that a being must exhibit in order to be subject to moral assessment is freedom. We frequently take as an excuse for morally bad behavior that the agent was not really free not to act badly; such excuses function by claiming that the conditions under which the agent acted preclude the agent’s behavior from being used as a basis for morally assessing the agent. Generalizing from thoughts such as these, it is plausible to hold that God is subject to moral assessment – including the assessment ‘perfectly good’ – only if God acts freely. And even apart from the connection between being free and being subject to moral assessment, it seems to be a great-making feature of a being that its agency is free agency. (See the entry on divine freedom.)
It seems, then, that we must think that God is free. There seems to be no conflict between holding that God is free and that God is perfectly good. A free being may have a perfectly good set of desires, slate of character traits, and career of actions. It may even be true that every counterfactual about what that agent would freely do were circumstances somewhat different involves that agent’s agency being perfectly good. But there may be a conflict between holding that the agent is free with respect to issues of moral relevance – what has been called being “significantly” free (Plantinga 1979, p. 166) – and being necessarily perfectly good. For many hold the view that freedom of action involves a capacity to act otherwise – that if an agent is free with respect to φ-ing, then it is possible that A φs and it is possible that A refrains from φ-ing. But if freedom involves the possibility of acting either way with respect to matters of moral relevance, then a free being cannot be necessarily perfectly good. For there is no possible world in which a necessarily perfectly good being acts wrongly; but for every significantly free being there is a possible world in which that being acts wrongly.
Maybe if the Trinity "is Love [or rather Agape?] Itself," as some would say, then we might go on to try to derive the other "properties" of God from this base, seeing love as a form of knowledge, power, and goodness. Then at least in this sense, the God of Love is necessarily good as such?
But unfortunately or not, Christians often try to say things about the ultimacy of the divine nature that make those kinds of extrapolations much more difficult to describe. The doctrine of divine simplicity is a, or even the, case in point: the best that anyone's ever done to reconcile God sustaining exactly one monadic divine predicate with the plurality of the divine Persons, is what Aquinas argued, that the Persons are polyadic predicates, relations, of the one divine nature to Itself (and each other). Whether this absolutely comports with the intended image of the simplicitarian God, I don't know, seeing as I don't know that the doctrine in question is true, and I might even be willing, if pressured, to say that I know that this doctrine is false. However, that is another story for another time...
Another option is to imagine that for God, there is some sort of thing we might call "super-goodness":
This is not to suggest that Henry [of Ghent] denies positive attributes in the more general sense of positive attributes inherited from the previous philosophical tradition, however. Henry grants positive attributes according to the Dionysian way of pre-eminence and the Anselmian method of attributing pure perfections to God, but these perfections are qualified by the addition of the prefix “super”. An example of this is the modification of “goodness” into “super-goodness.” This modification, however, signifies excess, and by it humans do not understand what they signify, rather only what they intend to signify.
If we do not understand, and if it is perhaps not even for us to understand, divine "super-goodness," it is less clear what it would mean to question whether God is necessarily "super-good."
