The Two Garments and the Two Tablets
Among the priestly garments discussed in this week’s parsha are the Choshen (Breastplate) and the Ephod (Apron). The Torah states: “They should fasten the Choshen by its rings to the rings of the Ephod with a turquoise cord, so as to be upon the band of the Ephod, and the Choshen will not move off the Apron.”
We have to understand why the Torah was so insistent that these two garments, the Breastplate and the Apron, should not separate from each other.
One simple approach is based on the Talmudic statement that the Breastplate, which the Torah characterizes as “the Breastplate of justice,” was atonement for [the perversion of] of justice, and the Apron served as atonement for idolatry. This The requirement to keep them attached was intended to dispel a specious and destructive belief that we can separate the commandments that deal with our relationship with G‑d from the commandments that deal with our social obligations. This separation can go in both directions. One can think that he or she can be pious and then cheat in business or  commit similar crimes against our fellow human beings. Conversely, a person can be honest and upright in his or her dealings with others and fail to show reverence for G‑d.  
To dismiss the notion that we can treat these two sets of obligations separately, the Torah required that the two garments not be separated but joined by a turquoise thread.
In truth, this lesson was not novel. It was derived from the Two Tablets that Moses brought down from Mount Sinai. The first Tablet deals with our obligations to G‑d and the second one deals with our responsibilities to our fellows. These two Tablets were placed together to indicate that they are equally important and interdependent.
The commandment not to allow the two garments to separate was intended to reinforce the lesson received at Sinai when Moses brought down the Tablets. Moreover, it strengthened the message because the Two Tablets were not attached  to each other, whereas the Ephod and the Choshen were.
Choshen and Ephod=Moshiach and Amen
The word Choshen has the Gematria (numerical value) of Moshiach (358) and the word Ephod has the Gematria of Amen (91).
The connection between Moshiach and the Choshen is found in the words of the prophet Isaiah, “Zion will be redeemed with justice…”  By respecting the rights and interests of others we will hasten the Redemption through Moshiach, who is the ultimate role model for righteousness as stated in Isaiah, chapter 11.
How does the Ephod connect to the saying of Amen?
At the end of Tractate Nazir, the Talmud tells us that saying Amen after one hears another recite a blessing is analogous to fresh troops who are deployed at the end of a battle in order to procure a victory. Hence, the recitation of Amen symbolizes the end of the struggle with the forces of idolatry, which symbolize all the evil and destructive ideologies that pervade the world throughout the period of Galus-exile. Moreover, by saying Amen after a blessing, we suggest that the Divine forces generated by a blessing (the word for blessing in Hebrew, beracha also means to elicit and generate), are finally absorbed and internalized within the world. The world will finally be permeated with Divine consciousness which will eliminate every trace of even the most subtle forms of idolatry. This will be the final and complete victory of good over evil.
To get out of exile, which came about through the destruction of the Two Temples, we need both justice and the elimination of all vestiges of idolatry. The first Temple was destroyed primarily because of idolatry and the second Temple was destroyed because of a lack of justice and Jewish unity.
The message of Choshen-Moshiach-righteousness fused with Ephod-Amen-victory is that we must intertwine the performance of our obligations to G‑d with the performance of our obligations to our fellow human-beings.
Redefining Idolatry
The Chassidic work Chaim Vsholom, by the pre-Holocaust Hungarian Sage, known as the Rebbe of Munkatch, provides another explanation for the need to keep the Ephod fastened to the Choshen.
As mentioned earlier, the Breastplate, which the Torah characterizes as “the Breastplate of justice ,” was atonement for [perversion] of justice, and the Apron served as atonement for idolatry.
What constitutes idolatry?
In Biblical times an idol worshipper deified a piece of gold, silver, wood or stone.  Today that form of idol worship is an anachronism. In the modern age, idolatry is the denial of G‑d’s existence, His providence and, indeed, all of the 13 Principles of Faith, articulated by Maimonides, including the belief in the coming of Moshiach.
Hence, idolatry today does not involve physical acts of devotion such as bowing to an idol, offering sacrifices or incense to a pagan deity. Instead, the modern form of idolatry resides in a person’s heart and thoughts. And although G‑d does not hold us accountable for bad intentions and thoughts, the Talmud (end of Chullin) states that the thought of idolatry is an exception to that rule. The Talmud adduces support for this from the verse in Ezekiel (14:4-5): “Every man…who will bring up his idol in his heart….I, G‑d, will respond to Him… to uncover the secret thoughts which he harbors in his heart.”
This then is what the Breastplate placed on the heart was intended to atone for. It is the way people judge G‑d in their hearts that is in need of correction. When the High Priest wore the Choshen it would generate a spiritual energy that would penetrate the hearts of those Jews who harbored doubts concerning the existence of G‑d and the13 Principles of Faith.
This explains the need to connect the Choshen to the Ephod. The Ephod was intended to atone for people who actually physically practiced forms of idol worship. However, the Ephod on its own did not suffice to procure atonement for those who practiced idolatry as long as they still harbored idolatrous thoughts. To achieve full atonement for idolatry one had to purify one’s heart and thoughts from all of the beliefs that compromise the fundamentals of our beliefs about G‑d.
Belief in Moshiach Connected to Belief in G‑d
The Munkatcher Rebbe, however, does not explain why the denial of Moshiach is considered idolatry.
The following is a possible explanation:
When a person would worship an icon, he or she was essentially declaring that G‑d does not exist or that G‑d is no more than a finite creation, the antithesis of G‑d. And although we cannot know G‑d we can know what He isn’t. In truth G‑d is not he or she. We just have no other way of communicating so we use human pronouns, knowing that G‑d is neither male nor female. G‑d is not human or physical; nor is He even a finite spiritual entity. To recognize G‑d as having competitors or partners is to render Him finite, which is tantamount to denying His existence. To believe that G‑d is like a created being in any shape or form is a denial G‑d’s true existence.
Thus, any belief that compromises G‑d’s transcendence over all of existence and His exclusivity is, by extension, a repudiation of the belief in the only, real G‑d.
It is therefore clear that belief in G‑d, the first of the 13 Principles of Faith, incorporates the belief in G‑d’s exclusivity and His incorporeality. 
13 but One
Upon deeper reflection we will see that all of the 13 Principles are extensions of the belief in an incorporeal and indivisible G‑d, particularly belief in the Divinity, immutability of the Torah, and belief in Moshiach.
If one were to posit that this world which G‑d created also fundamentally contradicts G‑d, that would be a blasphemous view. How could G‑d’s own creation go against its Creator who is perfect? We therefore come to the logical conclusion that G‑d has a plan for this world and that although the world seems to be a jungle, He gave us the means to transform it into a veritable garden, a world that reflects G‑d and His values. This plan, G‑d’s Master Plan, was revealed when he gave the Torah to the world. 
Nevertheless, it is not enough to believe that G‑d gave us a perfect Master Plan if it cannot and will not be implemented. We are led, then, to the belief in Moshiach and the Redemption, because to believe in Moshiach is to believe that G‑d and His plan are perfect. As long as there is evil, pain, and suffering in the world, G‑d’s justice and hence His perfection is called into question. How could an omnipotent G‑d allow a world to go amok and defy everything that He stands for? That could lead to the heretical conclusion that G‑d is not in control of this world and hence that G‑d is imperfect, which is a form of idolatry.
The Inner Dimension of Belief in Moshiach
Belief in Moshiach thus means that we believe that G‑d’s justice will be validated and that the plan G‑d has for this world will come to fruition because it is G‑d’s plan. If G‑d is perfect, so too, must His plan be perfect and unassailable. Today, the world that G‑d created is not in sync with its Creator’s plan. In the Messianic Age, however, that will no longer be the case. As the prophet Zechariah states (14:9), “On that day G‑d will be One and His name will be One,” and many other similar verses.
This does not mean that the physical world will cease to exist. If that were the truth it would mean that G‑d and the physical world are incompatible, once again casting doubt on G‑d’s perfection and imposing limitations on G‑d. The Messianic Age will usher in a consciousness that allows us to see G‑d in both the spiritual and the physical dimensions.
It is this dual consciousness that the Choshen and Ephod were designed to foster.