"Look at how they lied against themselves" by making excuses with lies, "And lost from them is what they used to invent," meaning: the idols they worshipped were lost to them; they did not avail them in the least.
Muhammad said:
Whoever reads "rabbina" (our Lord) with the genitive case (al-khafd), it is by way of description and praise; and whoever reads "fitnatahum" (their excuse) with the accusative case (an-nasb), it is the predicate (khabar) of "takun," while the noun (ism) is "illa an qalu" (except that they said).