Rulers must be Christians, not Pagan Idolaters (Joshua 24:1, 14, 15)

Joshua 24

King James Version (KJV)

1 And Joshua gathered all the tribes of Israel to Shechem, and called for the elders of Israel, and for their heads, and for their judges, and for their officers; and they presented themselves before God. ...

14 Now therefore fear the Lord, and serve him in sincerity and in truth: and put away the gods which your fathers served on the other side of the flood, and in Egypt; and serve ye the Lord.

15 And if it seem evil unto you to serve the Lord, choose you this day whom ye will serve; whether the gods which your fathers served that were on the other side of the flood, or the gods of the Amorites, in whose land ye dwell: but as for me and my house, we will serve the Lord.

Comments:

One serious error today held by many Christians is that a civil ruler doesn't necessarily have to be a Christian. One of the most outrageous examples is the recent support by Christians for the Mormon idolater Mitt Romney. 

But Joshua would have none of this nonsense; instead, he calls forth Israel's leaders, including judges and their officers, who then "presented themselves before God"—of which Matthew Henry writes:

They presented themselves not only before Joshua, but before God, in this assembly, that is, they came together in a solemn religious manner, as into the special presence of God, and with an eye to his speaking to them by Joshua; and it is probable the service began with prayer. (Matthew Henry Commentary on the Whole Bible, Joshua 24)

Apparently, Joshua considered the office of civil ruler so important that in his solemn charge to Israel before his death, he implores civil rulers to serve God and forsake idolatry—apparently with Israel's benefit in mind. 

We see here, then, that rulers play an important role in national reform. And it won't do to say that this charge was just given to Israel, but that rulers today are not obligated to serve God. Not everything that God required of Israel was unique to Israel. Moreover, I doubt we want to say that God—Who shares His glory with no other—is no longer to be honored by rulers.  

In fact, Scripture says "He that ruleth over men must be just, ruling in the fear of God" (2 Samuel 23:3b). Note that this text does not specify ruling over Israelites in particular, but all men in general. And as Psalm 2 requires of every ruler of the earth:

Be wise now therefore, O ye kings: be instructed, ye judges of the earth.

Serve the Lord with fear, and rejoice with trembling. 

Kiss the Son, lest he be angry, and ye perish from the way, when his wrath is kindled but a little. Blessed are all they that put their trust in him. (Psalm 2:10-12)

The church of course can still function without godly rulers, but this doesn't mean that rulers (whether godly rulers, or at least those with a pro-Christian policy) cannot be a means to help the church. Isaiah 49 prophesies favorably of rulers assisting the church in the New Covenant era:

And kings shall be thy nursing fathers, and their queens thy nursing mothers: they shall bow down to thee with their face toward the earth, and lick up the dust of thy feet; and thou shalt know that I am the Lord: for they shall not be ashamed that wait for me. (Isaiah 49:23)

On this text, Matthew Henry writes:

Some of the princes of the nations shall become patrons and protectors to the church: King shall be thy nursing fathers, to carry thy sons in their arms (as Moses, Num. 11:12 ); and, because women are the most proper nurses, their queens shall be thy nursing mothers. This promise was in part fulfilled to the Jews, after their return out of captivity. Several of the kings of Persia were very tender of their interests, countenanced and encouraged them, as Cyrus, Darius, and Artaxerxes; Esther the queen was a nursing mother to the Jews that remained in their captivity, putting her life in her hand to snatch the child out of the flames. The Christian church, after a long captivity, was happy in some such kings and queens as Constantine and his mother Helena, and afterwards Theodosius, and others, who nursed the church with all possible care and tenderness. Whenever the sceptre of government is put into the hands of religious princes, then this promise is fulfilled. The church in this world is in an infant state, and it is in the power of princes and magistrates to do it a great deal of service; it is happy when they do so, when their power is a praise to those that do well. 2. Others of them, who stand it out against the church’s interests, will be forced to yield and to repent of their opposition: They shall bow down to thee and lick the dust. The promise to the church of Philadelphia seems to be borrowed from this (Rev. 3:9 ): I will make those of the synagogue of Satan to come and worship before thy feet. Or it may be meant of the willing subjection which kings and kingdoms shall pay to Christ the church’s King, as he manifests himself in the church (Ps. 72:11 ): All kings shall fall down before him. And by all this it shall be made to appear, (1.) That God is the Lord, the sovereign Lord of all, against whom there is no standing out nor rising up. (2.) That those who wait for him, in a dependence upon his promise and a resignation to his will, shall not be made ashamed of their hope; for the vision of peace is for an appointed time, and at the end it shall speak and shall not lie. (Matthew Henry Commentary on the Whole Bible, Isaiah 49)