An initial puzzle people often have in reading Malebranche has to do with miracles. Malebranche, of course, is an occasionalist: he holds that God alone is the true cause. All other things are occasional causes, and what that means is that on the occasions when they occur, God guarantees that an associated effect comes about. For instance, I may swing a bat at a ball, but I am not the real cause of the ball’s flying away, merely the occasion on which the true cause works.
If you thought about occasionalism in the abstract you might think that this position would be quite cozy with the idea of miracles. After all, God is the only true cause anyway, so there’s not really any problem with him working a miracle here and there. In Malebranche’s case, however, it is not so. This is because what God wills in Malebranche are general laws governing the world. In the case of the ball, God wills the laws of nature that govern motion; because God wills these laws, and because what God wills necessarily must come about (because He is the one true cause), the ball’s motion follows those laws. There are scholarly controversies about the exact way to understand the role of general laws in Malebranche’s system, but the importance of them is quite clear. They can’t help but have importance, in fact, because Malebranche is intensely focused on divine Order, which he thinks governs all things, to such a point that he is even willing to say that it constrains God himself. Order is the "living law of the Father"; it has the force of law even for God. And Malebranche is quite clear that Order requires that God act in the simplest ways, which means willing that things happen according to general laws.
But miracles, one might say, don’t fit into this very well. What, after all, is a miracle other than a deviation from general law. So one might think that Malebranche’s conception of Order requires that there be no miracles. And Malebranche, in fact, seems to be uncomfortable with miracles in this sense of being a unique event; it’s clear that he would explain many miracles, for instance, in terms of the general laws governing the acts of angels and the like. But there are miracles, like the Incarnation, that don’t seem to be explicable in this way (they have to be the result of what Malebranche calls "particular volitions" as opposed to "general volitions"). So is there room for such miracles in Malebranche’s conception of Order?
There is, although I’m not sure there is any room allowed for it at the purely philosophical level. The reason, remember, that Malebranche thinks God must act according to general laws is that Order has the force of law. Why does Order have the force of law? Because God loves Order. Malebranche thinks of Order in a Trinitarian way: Order is also universal Reason, and universal Reason is the second Person of the Trinity. So the reason Order has the force of law for God is that the Father loves the Son and does everything through the Son; the Son is the divine Order, so the Father does everything through Order. In general this means acting according to the general laws found in divine Order. But in the case of certain things, like the Incarnation, God is still acting through Order: the Incarnate Word is, in fact, Order Himself, and so even though the miracle is unique, it is still done for and with divine Order, although not according to a general law. (There are, however, general laws that God wills given that the Word is Incarnate, namely, the general laws of grace, even though the Incarnation is not itself something that results from the willing of a general law.) The reason underlying miracles involving the divine Word is the same as the one underlying the general laws of nature: God loves the Logos, the Word, the divine Order. So he wills general laws, and exceptions only when the exceptions are better ways of honoring the divine attributes as they are found in divine Order.
There are many more threads in the topic of Malebranche and miracles than this; it's a complex subject. But it's an interesting case of how Malebranche's Trinitarianism has an influence on his philosophical views.