How is the natural law linked to the eternal law of God? The latter is the source of the former. Read the previous post for some context pertaining to what follows.
The eternal law is identical with God’s creative wisdom and providential governance of the world, which are as radically interior to the world and everything in it as they are transcendent of that world. In this sense, then, everything in the world is an expression of God’s eternal law – his creative wisdom – and finds its true or complete identity only in that law and wisdom…
As Ratzinger points out, the consequence is that the world – created being – is saturated with divine reason, indeed is constituted by divine reason. According to this view, the world can never be understood as simply pre-rational (as not yet participating in, and embodying, logos) because its internal order shares in divine reason. Indeed, it is in itself an expression of divine reason.
The result is that the world is not simply matter with certain physical properties that confronts human reason as object. Rather, the world in all of its physicality is itself saturated with meaning for its highest fulfillment in specifically human being. When the mind engages being, in other words, it is engaging what is primordially rational.
— David S. Crawford, “Natural Law and the Body,” Communio XXXV (Fall 2008). Emphasis original.
“The world… is in itself an expression of divine reason.” “[T]he world in all of its physicality is itself saturated with meaning…” “When the mind engages being… it is engaging what is primordially rational.” Chew on that for a while.