'Theirs' in the Bible

For if you were cut out of a field olive-tree, and against the natural use were united to a good olive-tree, how much more will these, the natural branches, be united again with the olive-tree which was theirs?

Yes, it has been their good pleasure; and they are in their debt. For if the Gentiles have had a part in the things of the Spirit which were theirs, it is right for them, in the same way, to give them help in the things of the flesh.