The letter suggests that they assimilate into Babylon (Jer 29:4-29:7)

“The letter said.

‘Thus says Yahweh of hosts!

The God of Israel!

To all the exiles

Whom I have sent

Into exile

From Jerusalem

To Babylon.

Build houses!

Live in them!

Plant gardens!

Eat what they produce!

Take wives!

Have sons!

Have daughters!

Take wives for your sons!

Give your daughters

In marriage!

Thus they may bear sons.

Thus they may bear daughters.

Multiply there!

Do not decrease!

But seek the welfare

Of the city

Where I have sent you

Into exile.

Pray to Yahweh

On its behalf.

In its welfare

You will find your welfare.’”

Interesting enough, this letter is very favorable to the Babylonians. After all, it was going to the king of Babylon. Once again it is the classical Jeremiah oracle with Yahweh of hosts, the God of Israel, as the source of this letter. They were to build houses, live in them, plant gardens, and eat from their produce. They were to have wives and children. They were to take wives for their sons and give their daughters in marriage, so that they could become grandparents. They should multiply there, not decrease. In fact, they were to get involved in the city there by praying to Yahweh for its welfare. After all, if the city did well, so would they. This seems like a clear attempt to assimilate into the Babylonian culture and society.