Pure and simple, Christians support Israel because God declared this to Abraham in Gen 17 regarding the land of Canaan,
5 "No longer shall your name be called Abram, But your name shall be Abraham ; For I will make you the father of a multitude of nations.
6 "I will make you exceedingly fruitful, and I will make nations of you, and kings will come forth from you.
7 "I will establish My covenant between Me and you and your descendants after you throughout their generations for an everlasting covenant, to be God to you and to your descendants after you.
8 "I will give to you and to your descendants after you, the land of your sojournings, all the land of Canaan, for an everlasting possession ; and I will be their God."
Did God judge the Israelites/Jews for their sin, unbelief, and failure to keep God's covenant? Yes, God did, allowing their enemies to take their land away from them many times, the last dispersion occurring in 70 AD. But when this prophesy of Zech 12:10 is fulfilled, the Jews will be living again in the land God gave to Abraham and his descendants "for an everlasting possession."
"I will pour out on the house of David and on the inhabitants of Jerusalem, the Spirit of grace and of supplication, so that they will look on Me whom they have pierced ; and they will mourn for Him, as one mourns for an only son, and they will weep bitterly over Him like the bitter weeping over a firstborn."
The Jews are now in the land of Canaan to stay until this prophesy is fulfilled, and our Lord Jesus returns according to Zech 14,
2 For I will gather all the nations against Jerusalem to battle, and the city will be captured, the houses plundered, the women ravished and half of the city exiled , but the rest of the people will not be cut off from the city.
3 Then the LORD will go forth and fight against those nations, as when He fights on a day of battle.
4 In that day His feet will stand on the Mount of Olives, which is in front of Jerusalem on the east ; and the Mount of Olives will be split in its middle from east to west by a very large valley, so that half of the mountain will move toward the north and the other half toward the south.
5 You will flee by the valley of My mountains, for the valley of the mountains will reach to Azel ; yes, you will flee just as you fled before the earthquake in the days of Uzziah king of Judah. Then the LORD, my God, will come, and all the holy ones with Him!
I for one do not want to be a part of those nations who come to fight against Israel and the Lord!