That IMHO is a very poor translation. Back in 2005, I had considered this passage from Romans and after considering the interlinear and prophecies concerning Israel, I penned the following in the footnote: -
Romans 11:25-27: - 25 Lest you be wise in your own conceits, I want you to understand this mystery, brethren: a hardening has come upon part of Israel,
until the full number of the Gentiles come in,[1] 26 and so all Israel will be saved; as it is written,
"The Deliverer will come from Zion,
he will banish ungodliness from Jacob";
27 "and this will be my covenant with them
when I take away their sins."
[1] This is a traditional understanding; however, I would suggest that a better understanding is made with reference to Daniel 8:13-14 and the trampling of the Sanctuary and God’s earthly hosts, by the heathen Gentiles and Exodus 20:4-6 which tells us that the iniquities of the fathers of Israel during the first two ages of Israel's existence will be visited upon the fathers' children and the children's children during the third and fourth age of Israel's existence.
A better translation would be: - “
until the prophesied full time period of the ‘heathen’ Gentiles is completed, after which, those of Israel will be saved;”
Hosea 6:1-3 and Lamination 5:19-22 confirms this understanding, but it requires a sound understanding of the Scriptures and the right Biblical context.