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)
Ba'al ha'Turim: And the Parshah of Erchin comes to atone for all the Kelalos.
This is not the great commentator on Shulchan Aruch (Shach).