Brakel builds his expectation of Israel's conversion not on one text alone.
After Romans 11 he goes through a whole row of Scripture passages. With this he wants to show that the same movement becomes visible from various sides.
2 Corinthians 3: the veil is taken away
Paul speaks of a veil at the reading of Moses and says that when one turns to the Lord, the veil is taken away. Brakel reads this not exclusively as a description of loose individual conversions, but as a text that fits within a future broad turning.
Yeshua over Jerusalem
Matthew 23 ends with judgement and a future-directed "until ye shall say, Blessed is he that cometh in the name of the Lord." Luke 21 speaks of times of the Gentiles. Brakel hears in that that the present state has a boundary and a future.
We must stay careful here. The texts each have their own context. Brakel reads them canonically together; that is a theological inference, not the same as saying that every text in isolation describes exactly the same event.
Isaiah, Jeremiah and Hosea
Isaiah 61 connects restoration, righteousness and recognition among the nations. Jeremiah 31 contains the new covenant with the house of Israel and the house of Judah and also uses cosmic language to stress God's abiding relation to Israel. Hosea 3 draws a long time of deprivation followed by return and seeking the LORD and David their king.
For Brakel such texts form a pattern: judgement is real, dispersion is real, but the judgement is not exalted into the last word about the nation.
The Messiah stays central
Brakel's expectation is no return to a religious status quo without Christ. In all his argument "conversion" means that Israel acknowledges Jesus as the promised Messiah. With that his christological ground from chapter 4 remains decisive.
From conversion to land
After section 31 Brakel takes a striking next step. He asks not only whether Israel will return spiritually, but also whether the Jewish nation will dwell in the land again. His answer is once more: yes.