Leibniz was a bit different from Spinoza in that he contended that matter is not real but only phenomenal. He further argued that God is purely a mental being, not a physical entity as in Spinoza's reasoning. Recall that Spinoza's view of God was that of Pantheism, God being identified with Nature.
Leibniz explained causality by proposing the existence of an infinite array of mind like entities, monads, each of which has a perception or a point of view on the whole world and which has a picture of the world with is correlated with the perceptions of other monads.
Interestingly, Leibniz said there is no interaction between monads but there is only correspondence in that each monad has its own history and one succeeds the other while also being aware of other monads.
He designated this relational concept between monads as "pre-established harmony."
According to Leibniz, God created, ordained and keeps everything going.
Therefore there is no need for causality in Leibniz' view. God causes everything, thereby eliminating the need for any notion of causality for Leibniz.
Regarding the place of freewill Leibniz argued on behalf of the omnipotence of God.
He contended that God created monads and equipped them with an intrinsic nature, which decides all that they do. Essentially and ultimately all that occurs roots in the omnipotence of God since the monad is equipped with a nature that determines everything they do.
Yet is also true that Leibniz believed in freewill to the extent that every individual is self-determining but it should be remembered that God has arranged for this in the structuring of monads.
