Romans 11:17-18
But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you.
Those rooted in Christ (believers - rooted in Him) are His Israel ... His church.
All are grafted into the tree (Christ) ... the natural branches are grafted into the tree as well as the wild ones.
Romans 11:24
For if you were cut from a wild olive tree, and contrary to nature were grafted into one that is cultivated, how much more readily will these, the natural branches, be grafted into their own olive tree!
The poster is correct ... all believers are His Israel ... His people ... His church ... grafted into the tree of life ... rooted in Christ.
May all be enlightened to this wonderful truth. Amen.