God has a form:

And the Father who sent me has himself borne witness about me. His voice you have never heard, his form you have never seen,( John 5:37).

Moses saw God's back:

"Then I will take My hand away and you shall see My back, but My face shall not be seen." Exodus 33:23

Angels behold God's face:

“See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven. Matthew 18:10

The appearance of God is described in Daniel 7 and it is the same appearance which Christ had in Revelation 1.

"The hair of his head was pure like wool" Daniel 7:9

"The hairs of his head were white like wool, as white as snow" Revelation 1:14

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"A Man clothed in Linen" Daniel 10:5

"A Man clothed with a Long Robe" Revelation 1:13

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"With a belt of fine Gold" Daniel 10:5

"With a golden sash" Revelation 1:13

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"His face like the appearance of lightning" Daniel 10:6

"His face was shining like the sun shining in full strength" Revelation 1:16

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"His eyes like flaming torches" Daniel 10:6

"His eyes were like a flame of fire" Revelation 1:14

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"His arms and legs like the gleam of burnished bronze: Daniel 10:6

"His feet were like burnished bronze, refined in a furnace" Revelation 1:15

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"The sound of his words like the sound of a multitude", Daniel 10:6

"His voice was like the roar of many waters" Revelation 1:15

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"I fell on my face in deep sleep with my face to the ground" Daniel 10:9

"When I say him I fell at his feet as though dead" Revelation 1:17

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"And behold a hand touched me and set me trembling on my hands and knees" Daniel 10: 10

"But he laid his right hand on me…" Revelation 1:17

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"Then he said to me, Fear not" Daniel 10: 12

"…Saying, Fear not" Revelation 1:17

The Torah says, "you saw no shape or form, you only heard a voice" (Deut. 4.12), The book of Isaiah says, "Before me no god was formed, nor will there be one after me." (43.10) King Solomon said, "But will G-D really dwell on earth? The heavens, even the highest heaven, cannot contain you. How much less this temple I have built!" 1 Kings 8:27 "The L-RD wraps himself in light as with a garment; he stretches out the heavens like a tent." Psalms 104.2

The Christian scriptures refers to G-D as: a) the invisible G-D (Colossians 1.15) b) as Spirit which must be worshipped in spirit and truth (John 4.24), c) as a consuming fire (Hebrews 12.29), d) dwelling IN unapproachable light (note: but is not that light) (1 Timothy 6.16); and, e) as greater than Yeshu 1 Corinthians 15.28.

I think the answer is implied in this command:

You shall not make for yourself an idol in the form of anything in heaven above or on the earth beneath or in the waters below. (Exodus 20:4, NIV)

When we imagine God to have a form we make an idol in our mind, when we carve this image into wood or stone then we make that idol visible.

The reason why imagining a form is idolatry is because God is immense, infinite and boundless, and any boundary or form we imagine limits God's limitless glory and is therefore an unholy thought that does not ascribe due glory to God. ‘Infinite’ essentially means that nobody can grasp it.

Does God have no shape or form?

Objection 1

The book of Genesis uses these words to describe man's creation

“Let us make man in our image, after our likeness. (Genesis 1:26 NIV)

therefore, God must look like man.

Objection 2

Throughout the Old Testament, the Spirit of God has appeared as moving flames, columns of fire and burning bushes. Columns of clouds, wind passing over the waters and smiting cedars, and the tiniest whisper. In the New Testament He came as tongues of fire above the heads of the Apostles. Therefore God must have some elemental form.

Objection 3

God has appeared to man as a visitor come to dine with and bless Abraham and his family; A stranger who would wrestle with Abraham's grandson Jacob; and finally as Jesus, the only Son of the Father.

On the contrary God has no physical body, therefore no shape.

I answer that even though God chooses to appear as someone or take on a form, it is not His shape nor His nature that has any form. The shape God chooses to take is not His shape. An ogre desiring to impress a clever kitten may take the form of the mouse, but the form of the ogre is still ogreish.

Reply to Objection 1 The Ox Says God made a spiritual image to Himself in man. The image which God made man in was after God's spiritual Self, not His physical Self (which doesn't need to exist).

Reply to Objection 2 God is made manifest in more than just flames and smoke. His character is impressed on us at Baptism, confirmed in us soon after and with us for a time when we consume His body, blood soul and divinity in the Holy Eucharist. God is not further from us than He was from the Israelites or the Apostles and we can't see His shape any better than they can, for it still takes the eyes of faith to see Him. After the Apostles received the Holy Spirit, some took them for drunkards, others seeing it was too early for drunkards to be roaming about saw, with the eyes of faith, that these men had the Holy Spirit about them and were Baptized soon after

Reply to Objection 3 The means by which God occasioned to visit the Patriarchs is not ours to judge, but we can hardly assume that He spent the rest of His time milling about the desert. Chances are very good that He passed from place to place as Jesus did, after His resurrection, coming upon the Apostles suddenly, making Himself known occasionally and leaving (or rather, disappearing) at just the right moment. One thing we believe about the Trinity is that all parts are equal in glory; Father Son and Holy Spirit. So, if the Second Person of the Trinity, Jesus, was some how created to be the only one with a fixed form, He would be the only one encumbered, as we are, with a fleshly body that puts our soul in one place at a time. Jesus, begotten, not made and consubstantial with the Father must have the same form as the Father and the Holy Spirit. And, as I said in the reply to Objection 1, it doesn't follow that because Jesus "took on the form of a servant" that His form is that of a servant from the start

Mainstream Christianity - Catholicism, Orthodox, and the various Protestant denominations, God doesn't have a form. He is spirit, omnipresent, and not confined to a single place. He doesn't have a form. (Although He could manifest one and speak through it, such as a burning bush...)

Of course, when He came to earth as Christ (as mainstream Christianity believes) He had a body of flesh.

The above is true of most denominations and traditions within Christianity.

A few denominations do, however, believe that God has a physical body. (One such example, the LDS Church teaches that He has a perfected physical body of flesh and bone).

God is the Father of our spirits.3 He has a glorified, perfected body of flesh and bone.4 We lived with Him in heaven before we were born.5 And when He created us physically, we were created in the image of God, each with a personal body.6