This is the heresy of Monophysitism (5th Century)
Monophysitism originated as a reaction to Nestorianism. The Monophysites (led by a man named Eutyches) were horrified by Nestorius’s implication that Christ was two people with two different natures (human and divine). They went to the other extreme, claiming that Christ was one person with only one nature (a fusion of human and divine elements). They are thus known as Monophysites because of their claim that Christ had only one nature (Greek: mono = one; physis = nature).
Orthodox Catholic theologians recognized that Monophysitism was as bad as Nestorianism because it denied Christ’s full humanity and full divinity. If Christ did not have a fully human nature, then he would not be fully human, and if he did not have a fully divine nature then he was not fully divine.
To think about God and reality the way the Church fathers did, you have to be able to put the infinite and the finite together.
This is why we believe that there are two natures but one person. It is a sacramental structure.