As per dictionary.com, here are two of the definitions of "mandate":
- a command from a superior court or official to a lower one.
- an authoritative order or command: a royal mandate.
Keep that in mind. Now, as david brainerd mentioned, the International House Of Prayer (IHOP) has a page named "Israel Mandate". As there are only a couple paragraphs, I'm going to go ahead and copy-paste the whole thing here.
Our mission is to mobilize intercessors in the Church to pray for Israel, and to stand with and encourage Messianic believers in Israel.
The International House of Prayer is committed to seeing the nation of Israel walking in their full destiny at the end of the age. Our primary role is to pray for and partner with Messianic Jews who are living in Israel. The operation and visitation of the Spirit in Israel is a vital part of releasing the great end-time harvest among the nations (Ezek. 36:23–36). However, this full release will only come as a result of a body of believers who are committed to a life of night-and-day prayer and fasting.
The "Messianic Jews" part tipped me off, so I made a Google search with those terms included. Most of the results that came up had to do with IHOP, though they were different branches. Here are a couple of them along with selected quotes:
IHOP: Eastern Gate
The International House of Prayer: Eastern Gate's Israel Mandate is being set in place to mobilize to pray and stand with the Jewish people regionally, nationally and spiritually.
Our confidence is that believers being filled with the Spirit of the L-rd will stir Israel to embrace Yeshua/Jesus as her Messiah. In return, God will use Israel as the instrument to bring restoration to the earth at the end of the age.
The strategy of this reality is in the building up of a network of prayer and partnership with the local Messianic Jewish communities and churches in the region. The key to this network will be Messianic prayer sets geared towards specifically praying for the salvation of the Jewish people and the restoration of Israel.
Cincinnati House of Prayer
One of our specific assignments at the Cincinnati House of Prayer is to partner with and stand for Jesus’ purposes concerning Israel and the Jewish people in our region and beyond. We do this by praying, mobilizing and teaching on Israel and standing with and encouraging Messianic believers in our region and throughout the earth.
Ways we Stand at the Cincinnati House of Prayer for the Purposes of God Concerning the Jewish People and the Nation of Israel
We intercede with prophetic acts of prayer, worship, love and justice
We partner with our Messianic Jewish brothers & sisters for God’s purposes and glory in the Tri-state region and on earth
We reject Anti-Semitism, Replacement Theology and other false teachings concerning Israel and God’s purposes for the Jewish people
We encourage the release of resources (time, talents and treasures) unto the purposes of God concerning the Messianic Jewish people, the nation of Israel and those desiring to return to Israel.
We strive to nurture and build-up our Messianic Jewish brothers & sisters in the Body of Christ
Finally, if you really want to learn a lot more, IHOP has a Israel Mandate Resources page that has many audio files from their Israel Mandate Conferences.
So, to sum up, the Israel Mandate seems to be the belief that we Gentile Christians are commanded by God to pray for Israel and to work with Messianic Jews. The goal is to bring more Jews to Christ, which continues Jesus' and Peter's work as well as honors the position that the Jews have as the chosen people of God. There seem to be other attached beliefs, but so far as I can tell, that is the core of the Israel Mandate: pray for and reach out to the Jews in Israel.