Gen 1:[26] And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.
[27] So God created man in his own image, in the image of God created he him; male and female created he them.

The Bible tells us the mystery of godliness is great (1 Ti 3:16). So it stands to reason men will have a difficult time understanding the doctrine of the Trinity. The word Trinity does not exist in the Scripture but without a doubt the doctrine does exist.
First, to reject the doctrine one must reject the KJV Bible, which indeed is the Word of God. The Bible clearly states God made man in His plural image. Note the words US and Our in Genesis 1:26 yet the very next verse uses the words HIS OWN for the very same distinction.
In order to have a greater grasp of this one only has to realize that man himself is a triune being. Let me write this again, MAN IS A TRIUNE BEING. What puzzles me are those that seem to grasp and believe man is a triune being but think God, in Whose image we are created, is not.

In 1Thes.5:23 we find:
And the very God of peace sanctify you wholly; and I pray God your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ.
I am not sure it gets any clearer than this. Man is a walking breathing three part being. We are composed of body, soul and spirit. Soul and spirit though intertwined are distinct and separable. according to Hebrews 4:12
For the word of God is quick, and powerful, and sharper than any twoedged sword, piercing even to the dividing asunder of soul and spirit, and of the joints and marrow, and is a discerner of the thoughts and intents of the heart.

The difference between our three parts and the Godhead’s is ours exists encased in our body (for now) while the Godhead exists separately.
So then, God is indeed three. Think of it this way.
God the Father = soul
God the Son = body
God the Holy Spirit = spirit
Here we have all three. All distinct yet all one. All God. So then man created in the plural image of God indeed is three parts: body, soul, and spirit.