Q:

Why isn't the cross considered an idol?

Exodus 20:1-15 ESV
And God spoke all these words, saying, “I am the Lord your God, who
  brought you out of the land of Egypt, out of the house of slavery.
  “You shall have no other gods before me. “You shall not make for
  yourself a carved image, or any likeness of anything that is in heaven
  above, or that is in the earth beneath, or that is in the water under
  the earth. You shall not bow down to them or serve them, for I the
  Lord your God am a jealous God, visiting the iniquity of the fathers
  on the children to the third and the fourth generation of those who
  hate me, ...

and

Leviticus 26:1 ESV 
“You shall not make idols for yourselves or erect an image or pillar,
  and you shall not set up a figured stone in your land to bow down to
  it, for I am the Lord your God.

How is this different than a Cross in a church?
I don't see how this cross
 is different than this idol .

A:

The difference is that a cross in a church is not worshipped. As the translators' notes in the New English Translation (NET) Bible indicates, regarding Exodus 20:4, the concern of the Law with respect to pesel—the Hebrew term referring to "an image that was carved out of wood or stone"—was about statues that "would be made for the purpose of worship, an idol to be venerated, and not any ordinary statue." In John Gill's exposition of this verse he makes the same distinction, that God's commandment regarded things shaped from wood or stone, cast into a mold, or engraved by men "in order to be worshipped." There is no compelling reason to think that the Law was opposed to any and all images whatsoever; after all, God himself commanded Moses to make a snake and set it on a pole, so that all those who were bitten if they looked upon it would live (Num. 21:4-9). As Gill notes, the Jews of Christ's era had no religious aversion to coins impressed with images, although "they vehemently opposed the setting up any images of the Caesars or emperors in their temple, because they seemed to be placed there as deities, and had a show of religious worship" (emphasis mine). Nor is there any compelling reason to think images were forbidden for use in worship—such as a cross in a church?—for were there not golden cherubim set over the Mercy Seat, which God commanded be made? As noted in the Jamieson-Fausset-Brown Bible Commentary, "The mere making was no sin—it was the making with the intent to give idolatrous worship" (emphasis mine), which is surely indicated in the rest of this second commandment, particularly as seen in verse 5: "You shall not bow down to them or serve them, for I, the LORD, your God, am a jealous God." The same thing is seen in Lev. 25:1, where the same worship qualification is found: "to bow down before it."
As described in The Christian Observer (p. 41)

It is manifest also that the art of the graver, sculptor, and embroiderer, was sanctified under the old dispensation. Still there is that sweeping intolerance of the second commandment towards any image or likeness of any created thing wherever or whatever it might be. But it scarcely needs much knowledge of the Hebrew idiom to be aware that when two clauses are paired together as in that commandment, "Thou shalt not make … Thou shalt not bow down," it does not mean two precepts but one. In most other languages the meaning would be conveyed something to this effect, "Thou shalt not make … in order to bow down thereto." If thou make for other purposes, the commandment touches thee not. So Calvin with his usual acute perception comments thus: "There is no necessity to refute what some have foolishly imagined, that sculpture and painting of every kind are condemned here." Otherwise Solomon's lions and oxen and palm trees must stand condemned, and the positive command to cast the brazen serpent and to model the cherubim would be a scandal and a difficulty. It was thus [in this fashion] that John of Damascus, Gregory II, and others replied to the broad assertions of the Iconoclasts.
("Early image-worship in the church," The Christian Observer, No. 1 [London: Hatchards, 1877], 41.)
(Note: I originally had more links in here, pointing to where these things can be read online, but it seems I need a higher reputation before I can post any more than two.)

A:

It would seem that the Cross could, in fact, be used as an idol.  However, from my experience, that would seem to be the exception rather than the rule.  The Cross is simply a reminder.  I have never prayed to a Cross or have even cared whether one was displayed while I was worshiping.  It is merely a symbol, much like the icthus on the back of my car.  (Just to clear, I don't pray towards that either.)
It should be noted that the original Temple (and tabernacle) had objects inside them--none of which were to be worshiped.  These items included the table of showbread, the altar of incense, the ark of the covenant, the golden lampstand, etc.  Each of these had a noble purpose, but none of them were worshiped.
There is a pretty significant distinction between the crucifix (with the image of Jesus on the cross) and just a cross, however.  Many Protestants view this very specifically as an image of God, since Jesus is the eternal, pre-existent Son of God.  As a result, many Protestants will never use the crucifix in any decorations at all for the very specific reason that it has in it the image of God.
So, symbolism is not forbidden in Scripture, and there is a precedent for having symbolic things in a place of worship (lampstands => Light of the world, Showbread => Bread of life... the articles of the old Temple pointed to Jesus, the Son of God).
Still, most Protestants at least would have no problem at all having all the cross decorations removed from a church.  It's only symbolic, and we worship God with or without them.

A:

No Christian that I know of prays to the cross, nor considers that the cross of itself has any power (rather, it is Christ's death on the cross that has power), nor even considers the cross sentient!
So the cross is merely a symbol of our redemption, reminding us of the price Jesus paid to save us; nothing more.

