The Firstfruit is Christ, the Lump is Christ, the Root is Christ.
Christ is the firstfruit of the resurrection, not of God's people, the one olive tree, of which the branches are the people of God.
In botany, the branches do not proceed from the root, but from the trunk.
Proceed in the metaphor of the natural olive tree is about the proceeding of the people of God; i.e.,
the branches (God's people) proceed from the roots, the patriarchs (and spiritually ]I]through[/I] the trunk, Christ).
The NT people of God are in Christ, who is the trunk, as they are in the vine (Christ).
"Jews" are the NATURAL branches.
Gentile believers are the WILD olive tree.
If you can understand text, you will see there is only one olive tree of the people of God, from which tree the branch of Israel has been cut off, and the branch of the Gentiles has been grafted in (Ro 11:1-23).
The firstfruits of God one olive tree of the people of God were the patriarchs, Abraham, Isaac and Jacob, its holy (set apart) roots.
16 For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches [Israel].
17 And if some of the [natural Israel] branches be broken off, and thou [Gentiles], being a wild olive tree [Gentiles], wert graffed in among them, and with them partakest of the root [Christ] and fatness of the olive tree;
In botany, the branches partake of the root of the tree through the trunk, in which the branches "abide" (Christ).
18 Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee.
19 Thou wilt say then, The branches were broken off, that I might be graffed in.
20 Well; because of unbelief they [Natural Israel] were broken off, and thou standest by faith. Be not highminded, but fear:
21 For if God spared not the natural branches, take heed lest he also spare not thee.
22 Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off.
23 And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again. 24 For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree? Rom. 11:16–24.
And that's
IF, not "when," they do not persist in unbelief.