# if they do not continue in their unbelief

The phrase "do not continue in their unbelief" is a double negative. You can translate this in a positive form. Alternate translation: "if they start believing" (See: [[rc://en/ta/man/jit/figs-doublenegatives]])

# will be grafted in

Paul speaks of the Jews as if they were branches that could be grafted back into a tree if they start to believe in Jesus. You can translate this in an active form. Alternate translation: "God will graft back in" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-activepassive]])

# graft

This is a common process in which the end of a live branch of one tree is inserted into another tree so that the new branch will continue to grow in that tree.

# they ... them

All occurrences of "they" or "them" refer to the Jews.