It is said that whatever God does is good.
But you must understand why this is said. That whatever God does is good is so, not because “God did it”, but rather because God is internally consistent. That is to say, it is not the Divine Will that determines goodness, but the Divine Being itself. And because of God’s internal consistency, His actions deriving from who and what He is, His actions are therefore always good.
It is an Islamic proposition that goodness is determined by the Divine Will, not a Catholic one. Therefore, in Islamic theology, if God changes his mind about something, it is changed. What’s good today may be evil tomorrow, and vice versa, depending on the Will of Allah. This is part of the reason the theoretical sciences never developed very well in Islamic countries, though their practical sciences did well.
This is not the case in Catholic theology. Goodness is determined by the Divine Being, and since that does not change, goodness doesn’t change. This is why the theoretical sciences flourished in Catholic countries… because they are grounded in the understanding that the universe operates upon unchanging, universal principles, deriving from the Creative mind of an unchanging God.
So, God cannot simply say that lying is good, and it therefore is. When God created the world, He did not declare each of His creations good, and they were so. Rather, God saw His creatures and recognized their goodness. Why? Because they were good insofar as they manifested His own glory. They were good because they were
like God, each in their own way.
More specifically, lying is the expression of untruth. It is antithetical to being and to reality. As such, it is manifestly contrary to God, who is being and truth and the source of reality. To suggest lying is good is to suggest that to act contrary to God is good.
Are there occasions wherein lying may be justified? Maybe, but I think that’s a question for a different thread… unless it’s something you’d like to discuss here.