Creatio ex nihilo entails a good God
It is not uncommon to come upon the question: How can we know that God is good rather than evil? God's goodness has been called into question in less polite ways by extreme atheists which justify calling God sadistic by enumerating many sufferings that people experience in this life. I will not attempt a classic theodicy1 here, rather, I will take an approach that might be called apriori with respect to existence of particular evils. This means arguing for God's goodness from the nature of God and the world and their ontological relationship2.
Love does not delight in evil
Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres. -- 1 Corinthians 13:4-7
There are many senses in which people use the word "love" but the kind of love we are interested here is the love that is described in the above quote from St. Paul — the same love that Christ commands us to have. And in this commandment of Christ lies a paradox of sorts. If love is understood just as an emotion then how can it be a commandment, for emotions are spontaneous and not directly under our control. Furthermore, we know from our experience of loving our siblings, parents, spouses and children that we don't constantly have the exact same warm feelings towards them but we wouldn't say that we have stopped loving them because of that. Emotions come and go and come again, but our love for them persists throughout.
In order to make sense of the above it is better to think of love not as a particular emotion but as a type of relationship with others. Indeed, the very act of and readiness to give oneself3 for the good of the other is what I would call love. It is in this relationship that all the nice emotions we associate with the word "love" are caught up and generated.
The question remains whether the one who selflessly gives himself can in that very act have some evil purpose towards the recipient of his love? If there are ulterior motives for that act then the act is not an act of love and it is not selfless. To claim that an act of love can at the same time be an act of ill intent is a contradiction. The very concept of giving oneself foregoes any self-centeredness of the act. In that act I forget myself and all that remains is the other.
Creatio ex nihilo is Creatio ex Deo
For in Him we live, and move, and have our being. -- Acts 17:28
For those versed into theological doctrines the claim that creatio ex nihilo is creatio ex Deo might seem like a heresy, but bear with me for a while.
When we talk of God creating the world out of nothing, we should be careful to avoid substantiating this nothing. The Almighty God is not a demiurge which takes some pre-existing matter and molds it in order to create something particular. In this sense nothing is not a substrate on which God works to create something. More precisely, creatio ex nihilo might be characterized as creation not out of anything — there is not anything existing side-by-side with God that participates in creation in any way.
From the preceding clarification it follows that the only source of created things is God himself. So, creatio ex nihilo actually shows to be creatio ex Deo. In which specific way is everything created out of God I don't think is important for the task at hand. The important thing is that ultimately there is nothing but God and that this God gives Himself in order to create and sustain the world.
Creation is an act of love
Whoever does not love does not know God, for God is love. -- 1 John 4:8
Since creation is the act of self-giving of God it means that creation is an act of God's love. There is nothing that God can gain from this self-giving, since there is nothing at all besides Him. There is likewise nothing lacking in God that could be fixed (or a hole that could be filled) by having creatures, since all that creatures have comes from Himself. The only ones that stand to gain anything from the creation are the creatures themselves.
Just like a loving father is not evil to his children so the loving God is not evil to his creation. And even more so! The father might be evil to others but to God there is no other than the whole of creation which he made in his love.
Love created the world, Love sustains the world and Love will save the world.
An attempt to justify God's goodness in the view of existence of evil.↩
One common example of a similar type of argument is that evil is a lack of perfection or privation of good, so God being maximally perfect being cannot be evil since there is no lack or privation in Him.↩
One can give oneself in different ways: by giving away his own time, powers, possessions, even his own life.↩