In 1842, the Latter-day Saints had lost their first temple in Kirtland. They were constructing a second in Nauvoo when Joseph Smith wrote the words above, as well as the following:

Persecution has not stopped the progress of truth, but has only added fuel to the flame, it has spread with increasing rapidity, proud of the cause which they have espoused and conscious of their innocence and of the truth of their system amidst calumny and reproach have the elders of this church gone forth, and planted the gospel in almost every state in the Union; 

it has penetrated our cities, it has spread over our villages, and has caused thousands of our intelligent, noble, and patriotic citizens to obey its divine mandates, and be governed by its sacred truths. 

It has also spread into England, Ireland, Scotland and Wales: in the year of 1839 where a few of our missionaries were sent over five thousand joined the standard of truth, there are numbers now joining in every land.

https://www.josephsmithpapers.org/paper-summary/church-history-1-march-1842/4

In 2024, there are 411 missions around the world. "According to the Church’s end-of-year statistics, the 2021 total of full-time teaching missions was 54,539, with an additional 36,639 service missionaries. Those numbers are up from the end of the previous, pandemic-period year of 2020 — 51,819 and 30,527, respectively."

https://newsroom.churchofjesuschrist.org/article/area-breakdown-of-churchs-411-missions-worldwide 

In 2024, there are 335 temples in various phases around the world, although these numbers change frequently as new temples are announced and others begin construction. 

• 189 dedicated temples (with 184 operating and 5 previously-dedicated, but closed for renovation), 

• 52 under construction 

• 94 others announced (not yet under construction).