Rav Hirsch seems to understand that there’s no specific connection between Arachin and the Tochacha. Rather, the Sefer up to this point focuses on one general concept, while these last passages, beginning with Arachin, are fundamentally different – hence their position at the end, almost as an afterthought. In his own words (as translated by Feldheim):
The book of Vayikra teaches us our duty to the Sanctuary of the Torah. We are to symbolize through offerings and to realize in practice the sanctification of our lives as individuals and as a nation. And, finally, the preceding chapter states that the חוקים משפטים ותורות — which tell us what we must do in order to hallow our lives as individuals and as a nation — are the sole intermediaries of the covenant between ourselves and God, and the sole means for assuring our welfare.
Scripture now adds a concluding chapter on voluntary donations to the Sanctuary. A person feels the need or has the desire to give to the Sanctuary an object or its equivalent value, in order to demonstrate his special interest in the Sanctuary, or to signify the special relationship that — in his view — exists between the object and the Sanctuary.
These donations to the Sanctuary are called here הפלאת נדר (v. 2 כי יפליא נדר). They are not required by law, and do not stem from the requirements of the law. Rather, they spring purely from one’s own feelings.
It is characteristic that this chapter, which deals with donations to the Sanctuary, appears — by its position — merely as a supplementary concluding chapter. Scripture thus explicitly states that this chapter is not included among the חוקים משפטים ותורות, which God has set as the condition בינו ובין בני ישראל, and whose fulfillment will result in the fullness of blessing, and whose violation will bring about all the misery described in the preceding chapter. The donations to the Sanctuary are clearly separated from the חוקים משפטים ותורות, and this teaches us an important point:
תורת כהנים, the Jewish priestly code, does not attach special value to Sanctuary donations, and does not see in them special piety, especially pleasing to God. Certainly, then, it does not ascribe to them the power to atone for a sinful life. The Sanctuary of the כהנים sees its mission not in gaining possessions, but in gaining hearts and souls. It seeks to gain the whole of our lives — as individuals and as a nation — for the fulfillment of the חוקים, the משפטים, and the תורות. The sanctification of morality, the safeguarding of justice in society, the enlightenment of the mind and the ennoblement of the heart — the חוקים, the משפטים, and the תורות — they are the sole means of attaining God’s grace. It is they that mediate בינו ובין בני ישראל, and only they bring man closer to God, and God closer to man.