Rashi: You will serve Me from love, and not from fear. Ishi is an expression of Ishus (marriage), and fondness of youth. Bali is an expression of a master, and fear.

Rashi citing Pesachim 87a: Ishi is a Kalah in her father-in-law's house (i.e. after Nisu'in). Ba'ali is a Kalah in her father's house [during Eirusin].

Radak: A wife's husband is called Ish, e.g. "Elkanah Ishah" (Shmuel I, 1:8). Keneses Yisrael are compared to [Hashem's] wife. Ba'al applies also to idolatry ¹ . Yisrael will cease to call Hashem Bali, to remove 'Ba'al' from her mouth (19).

Malbim: Ba'al shows authority and acquisition ? he rules over the matter because it is his. Ish shows love, closeness and marriage. Until now, Hashem was not close to them; Hashgachah was hidden in the veil of nature. Yisrael served amidst fear, and called Him Ba'al because He ruled over them. Sometimes they look at His servants, which are means for the influence that He sends to Yisrael via them, and they fear and honor the servants. In the future, He will go among them, and give to them His Brachos without an intermediary, just like a man is secluded with his wife. His dwelling will be in the lower world, to make His honor dwell among them. You will receive Divine influence face to face and serve amidst love; you will not fear and honor anything else.