The phrase all Israel can be understood in more than one way. It may refer to all believers, both Jews and Gentiles. With this meaning, it describes how God brings salvation to all his people.
Another view is that all Israel refers to all Jews who will believe during the Christian era, or to a large number of Jews who turn to Christ in the last days. With this meaning, the word and so has a sequence. After the full number of Gentiles comes to Christ, then a large number of Jews will be saved. This phrase does not mean that every Jewish person will be saved(see 2:17–29).
In the Old Testament, the one who rescues (or delivers) is the Lord. Paul is almost certainly speaking about Jesus Christ here (see 1 Thessalonians 1:10).
from Zion: The Hebrew text of Isaiah 59:20 says, "The Redeemer will come to Jerusalem." Paul may have adjusted the wording to point to the first coming of Jesus from among the people of Israel. He may also be pointing to the future return of Jesus from the heavenly Jerusalem (see Hebrews 12:22).