Paul was enunciating the principle that everything created by God, conforms to and gives voice to His nature, man being the quintessential expression thereof. (Latin: "Imago Dei"). In "Let us make man," the only instance in the Creation narrative where the phrase appears, God expressed both his triune nature, and perfect oneness in voicing his will to make man. That God would fashion Eve out of one of Adam's ribs was never in doubt, for in order for Adam to be both one and "us" at the same time like God, Eve had to be taken out of Adam. God was an "us" so Adam would be an "us." When God brought Eve to Adam and the two became one flesh, Adam was still Adam only now he was an "us."
All of creation actively declares the glory of its Maker, for God cannot create that which by nature, contravenes His own.
Roughly two millennia after Paul's letter to the Romans, the Framers would enunciate the Apostle's teaching in the parlance of their own day, in appealing to "the Laws of Nature and of Nature's God" (LONANG), in the Preamble to the Declaration of Independence. Not since the Kingdom of Israel and the Mosaic Law, had a nation been founded upon the Laws of Nature and Nature's God. That the Laws of Nature have served as the foundation of American Law and Jurisprudence from America's inception, makes this nation unique indeed.
The Framers: "We hold these truths to be self-evident ..."
Paul: "For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made ..." (Romans 1:20a, KJV).
Paul was simply making the case that truth is as plain as the nose on our faces if we'll but open our eyes.