Eden is not just a garden for humans, but the garden of God, Is 51:3; Ezek 28:13.  As Wenham explains,

‘The garden of Eden is not viewed by the author of Genesis simply as a piece of Mesopotamian farmland, but as an archetypal sanctuary, that is a place where God dwells and where man should worship him. Many of the features of the garden may also be found in later sanctuaries particularly the tabernacle or Jerusalem temple. These parallels suggest that the garden itself is understood as a sort of sanctuary.’

Walton (DOT:P, art. ‘Eden, Garden of’) explains that if the entire creation is represented in these early chapters of Genesis as the Temple complex, then Eden is the holy of holies, and the garden the antechamber to the holy of holies:

‘With this understanding, it can be appreciated that in the aftermath of the Fall, the greatest loss was not access to paradise; it was access to God’s presence. The temple provided for a partial return of that presence, and the antechamber of the temple was reminiscent of the proximity to God’s presence that had once been enjoyed.’

Eden as a garden-temple is supported by the following:

(a) Eden was understood by the prophets to have been located on a mountain, as with all temples;

(b) the furniture of later temples corresponded with the imagery of Eden – the lampstand in the temple being a symbol of the tree of life, and the curtain of the temple being embroidered with cherubim;

(c) Eden was the place of God’s presence.  A number of such connections are made in Lev 26:4-13.

But the garden is not only a sanctuary in which God dwells.  Walton quotes Neiman:

‘It is also the source of all the creative forces that flow forth from the Divine Presence, that energize and give life to the creation in a constant, unceasing outflow of vivifying power’.

This idea of water flowing from the dwelling place of God occurs again in Eze 47:1-12 and, especially, in Rev 22:1f.

Greg Beale offers multiple reasons for considering the Garden of Eden to be the first Temple.  In Derek Rishwamy’s summary:

1. In the later OT the Temple was the place of God’s special presence where he made himself known and felt to Israel. That is exactly how his walking with Adam and Eve in the Garden is depicted. (Gen. 3:8)

2. Adam is placed in the garden to “cultivate (abad)” and “keep (samar)” it (Gen 2:15). The same two words are translated elsewhere “serve” and “guard”, and when they appear together, they are either referring to Israelites serving or obeying God’s word, or more usually, to the job of the priest in guarding and keeping the Temple. (Num. 3:7-8; 8:25-26; 1 Chron. 23:32) Elsewhere Adam is portrayed dressed in the clothes of the high priest, functioning as a high priest. (Ezek 28:11-19; see Beale, pg. 618 on this for more argumentation.)

3. The tree of life served as a model for the lampstand, which was clearly shaped as a tree, in the Temple.

4. Israel’s later Temple was made with wood carvings of flowers, palm trees, etc. meant to recall Eden’s garden brilliance  (1 Kings 6:18, 29, 32, 35); pomegranates were also placed at the bottom of the two stone pillars in the Temple. (7:18-20)

5. The entrance to the Temple was to the east, on a mountain facing Zion (Ex. 15:17), just as the end-time temple prophesied in Ezekiel is (40:2, 6; 43:12). Well, turns out the entrance to Eden was from the East (Gen. 3:24) and in some places pictured as being on a mountain. (Ezek. 28:14, 16)

6. The tree of the knowledge of good and evil and the ark of the covenant both were accessed or touched only on pain of death. Also, both were sources of wisdom.

7. Just as a river flowed out of Eden (Gen 2:10), so a river is supposed to flow out of the End-time Temple (Ezek 47:1-12; Rev. 21:1-2)

8. This one requires some serious argument so I suggest you consult Beale directly here (pg. 620-621), but just as there was a tripartite sacred structure to the Temple, Beale discerns a tripartite structure to creation with Eden standing at the center as a Holy of Holies.

9. Ezekiel 28:13-14 refers the Eden as “the holy mountain of God” which everywhere else in the OT is Temple and Tabernacle language.

Rishwamy suggests a number of implications:

Creation — Why did God create the world? To inhabit it and dwell with people.

Anthropology — If the Garden is the Temple, then Adam is a priest. That has implications for our idea of human purpose and our relation to the rest of creation.

Israel/Covenant — God sets apart a people of Tabernacle and Temple-makers, who take up Adam’s original commission.

Christology — When we start to realize that Christ is the greater Temple, fulfilling all that the Temple was supposed to be, as well as the true Adam, it starts to fill in the picture on the aim of Christ’s work.

Ecclesiology — It follows from our thinking about human purpose, and our idea of Christ’s work that our theology of the church will be impacted by this idea as well.

Eschatology — If our theology of creation is impacted, then so is our eschatology, because God will fulfill his purposes at the end of all things.