"But if you do not, then be informed of a war [against you] from Allah and His Messenger," meaning: know that you are at war with Allah and His Messenger, and that you are polytheists (mushrikun).
Muhammad said: Whoever recites it as "fa-adhinu" (without a connected alif) means it is from "adhana, yu'dhinu," meaning: to inform. Whoever recites it as connected ("fa'dhanu") means it is from "adhina, ya'dhanu"; if one listens to something and hears it. "But if you repent," meaning: if you embrace Islam, "you shall have your principal sums," meaning: the excess is nullified if it remained as a debt owed by the sought party. "You shall not wrong," by taking the excess, "nor be wronged," by having anything taken from your principal sums.