The Bible says that God created man in His own image (see: Genesis 1:27). God is spirit and therefore can't be worshiped by, or have fellowship with, a being that has no spirit. That's why God created man in His own image.

The image of God doesn't refer to man's physical body; it refers to the spirit that dwells within this body. Once again, God is spirit and not flesh. Of all the creatures in the world, man alone possesses a spirit. This is because man alone was created in order that he might be able to have a relationship with God and worship Him. The reason animals can't worship God is that they don't have a spirit. In Romans chapter 1 verse 19 it says,

It's the spirit within man that enables him to know God. The problem arises, however, when people, whether they believe in Jesus or not, don't understand the spirit. Even those who think there is a spirit within man don't really know what that spirit is.

Some erroneously assume that their spirit is their personality as expressed in their actions. They try to approach God through their intellect, emotions, or will, all of which are aspects of their personality. This, however, is absolutely impossible.

Some people acknowledge the existence of God intellectually and mistakenly think this is faith.

Some base their belief on emotions. They are excited by certain religious activities and take this as an indication of their faith. This is actually nothing more than a form of mysticism.

Some people resort to willpower as they make up their minds to believe and attempt to put into practice what they read in the Bible. Any success they may have is only the result of strength of will. Such is a religion of resolution.

People who base their faith on these various aspects of the personality don't realize that they haven't yet found the true way to worship God who is spirit.