Why does the Torah juxtapose the Parshah of Erchin next to the Kelalos?
Ba'al ha'Turim: Because the total of all the evaluations of the various Erchin adds up to 143, the equivalent of the 45
Kelalos in Bechukosai plus the 98 in Ki Savo.
(2): This is to show that the curses are not a punishment, rather, to refine Yisrael and enable them to endure forever, for Hashem cherishes and esteems everyone! Refer to 27:2:3:4.
This is like Midrash Tadshei. Many say that there are 49 curses here. (PF)
And the Parshah of Erchin comes to atone for all the Kelalos.
This is not the great commentator on Shulchan Aruch (Shach).