In the Ancient Near East it was common for a king to have images of himself dispersed throughout his empire. These images represented to the people his authority. In Matthew 6:10 Jesus says, “…your kingdom come, your will be done on earth as it is in heaven.” God is the sovereign King over the universe and is expanding his kingdom from heaven to earth. He chose humanity to reflect his glory here on earth. We are the king’s image dispersed throughout his kingdom. Offspring are considered to be the likeness of their father, the one who created. Humanity is the likeness of its Creator. Succinctly defined, the image of God is humanity having a nature that consists of first a rational being and second a body and soul, and functions as a reflection of God’s glory and his earthly representative.
Scripture declares that humanity is made in the image and likeness of God (Gen 1:26-27, Eph 4:24). How then does humanity function as a reflection of his glory? The answer is in humanity’s very nature: rational being and body/soul. To be a rational being is to have the capacity to know, will, love and act. Adam proved to be rational when he was given the task of naming the animals (Genesis 2:19). The Westminster Confession of Faith 4.2 professes that man was made as a rational, knowing being, “after God had made all other creatures, he created man, male and female, with reasonable and immortal souls, endued with knowledge, righteousness, and true holiness, after his own image….”. Scripture refers to this rational side of our nature as the heart. Oliver O’Donovan writes that we were created to “think God’s thoughts after him”. O’Donovan further suggests that our “creaturely reason…enables us to receive, process, understand, and willingly respond to divine revelation.” The second part of human nature is body/soul. The body/soul duality reflects God’s glory, righteousness and holiness. The prerequisite to this reflection though is the rational being part of human nature for humanity could never reflect God without having knowledge of him first (WCF 4.2). John Murray concludes that the body/soul duality is “separable in principle (Matthew 10:28, 2 Corinthians 5:8) but united in and for well-being (2 Corinthians 5:4, Romans 8).” The whole man, body and soul, are part of the image. Wollebius confirms that “the subject of the image is primarily the soul, and secondarily the body, in so far as the actions of the soul express themselves through the body.”
When human nature became sinful at the fall did humanity cease being the image of God? Paul denies this as he refers to humanity still as the image of God in his letter to the Corinthians (I Cor 11:7). How then is the image of God appropriately described before and after the fall? John Murray suggests there is a twofold aspect in the image of God, “one as intrinsic and the other as forfeited in the fall”. 
In Reformed Dogmatics, Bavinck clearly states that God is the archetype of man and Christian theology should use the following to decipher the image of God in man: 1) soul and body; 2) the heart as the center of all human faculties; 3) powers; and 4) gifts.  “All that is in God – his spiritual essence, his virtues and perfections, his immanent self-distinctions, his self-communication and self-revelation in creation – finds its admittedly finite and limited analogy and likeness in humanity.” – Bavinck
 Swain Lecture 1 Notes II.B.2.c.ii.
 Swain Lecture 1 Notes II.B.1.b.
 Wollebius, Compendium Theologiae Christianae, 65.
 John Murray, Collected Writings of John Murray Volume 2, 40.
 Bavinck, Reformed Dogmatics Volume 2, 554-561.