الْخَطَأُ ظَاهِرٌ؛ إِنَّ الْخَطَأَ لَظَاهِرٌ.
The error is clear; indeed the error is unmistakably clear.
Both express the same basic judgment, but the second intensifies it with “inna” and the emphatic lām. It may be more suitable when the listener disputes the error; the first can suffice when the matter is already accepted.
Advanced criticism avoids asserting that the more emphatic version is universally better. The better choice depends on what the audience already knows or contests.