ذَٰلِكَ الْكِتَابُ لَا رَيْبَ فِيهِ
That is the Book; there is no doubt about it.
Under one syntactic reading, “dhālika” is the subject and “al-kitāb” its predicate, yielding an independent assertion. The following “lā rayba fīh” excludes doubt concerning that Book, reinforcing the first statement.
This is a particular grammatical analysis, not the only possible parsing of the verse. Its relevance here is rhetorical: under that reading, the second clause intensifies the meaning of the first and can follow without coordinating wāw.