If you ever read Plato, it's not a surprise that Laws is not his best work. It took me quite a while to get through it and the overall impression is .. mixed. The flow of the dialogue is boring: the Athenian preaches to his two companions, sometimes the details are excessive (how many minae would be the penalty of giving a false statement of you are rich/middle class/poor) and sometimes an argument is given without too much justification (the population of a city should be exactly 5040 because it's a nice number).
Let's try dissect a part of Laws. This argument is sprinkled a bit here and there within the dialog but it goes like this: virtue is the basis of laws and laws are there to uphold virtuous behaviour (and obviously prevent vice). Laws should cover every aspect off social interactions of a city (at least it seems so) including religious rites and practices, organization of city administration and courts, trades (Plato does not like tradesmen a lot) and family/inheritance. Some of the "degrees" given by the Athenian even resemble the Old Testament (who should marry a widow and take care of her children).
Plato was getting old while writing Laws and that may explain his support of tradition. All dances, hymns and poems must be presented exactly as they were, no changes allowed. It's morally (and probably legally) wrong to be an atheist. A big part of the authority of the state/city lies on its similarity with a human being who has a soul that is obviously divine. The argument is kind of weak here. We must believe that humans have a soul because we are rational. Moreover, heavenly bodies have souls, too, otherwise they would not move. And since we admit that the sun has a soul, we somehow must believe that it is divine. Thus, gods exist. And everyday experience shows that they are interested in humans. Thus: follow the religious practices of your city (or they might be displeased).
Let's say something about the organization of the book (actually Laws consists of 10 books). The Greeks established cities and colonies. In the first book the Athenian discusses how a city should be founded. Then the discussion for a while falls into the first principles of laws (see the previous paragraph) and covers land usage, temples and families. This dialogue has a long discussion about education, too.