God has an eternal purpose for Israel: to be a light to the nations (Isaiah 42:1-9). Through Israel all families of the earth will be blessed (Genesis 12:2-3; 22:14-18). The promise continues to Isaac (Genesis 26:4-5) and Jacob (Genesis 28:14). God has not, and will not, change His plan and purpose for Israel (Romans 11:29).
God will fulfil His purposes in Israel: 'I am with you and will watch over you wherever you go, and I will bring you back to this land. I will not leave you until I have done what I have promised you' (Genesis 28:15). In Isaiah 43:1-13 God speaks of Israel being His servant, for His glory, chosen to be a channel of His revelation and glory to the nations.
God is a God of covenant - Exodus 34:5-14.
God has called Israel to be a kingdom of priests (Exodus 19:3-11). His covenant with Israel will not be broken as long as the earth's systems exist (Jeremiah 31:27-37).
The Gentiles are called to be an important part in Israel's re-gathering and restoration - and also to provoke them to jealousy (Romans 11:13-14; Jeremiah 31:1-14; Isaiah 49:22-26; 60:1-15; 66:7-21).
Israel shall be restored and grafted back into their own olive tree - so that God's name will be hallowed in Israel (Romans 11:13-16; Ezekiel 36:16-36).
The Church is only complete as Israel and Gentile believers become the 'one new man' and become an instrument of God in the end times (Ephesians 2:11-22). John 17:21 is actually about the unity of believers - Jew and Gentile. John 10:16 refers to 'other sheep that are not of this sheep pen' - the Gentiles.
The fulfilment of God's purposes for Israel is a preparation for the coming of Messiah. We are living in very important days and now is the time for laying and building on the foundations of the ministry to be an increasingly effective instrument of the Lord worldwide.