In many immigrant families, it's inevitably the case that children find it much easier to assimilate into their new country than their parents. This is not really surprising; parents are older and more set in their ways. They thus often find it hard to adapt to life in a new country, especially one with a completely different culture.
And that's certainly the case in The Namesake. Though Ashoke and Ashima have moved to the United States, they remain wedded to the old rituals and traditions of the Bengali community. These aspects of Bengali culture are all the more important to them now that they are separated from their relatives thousands of miles away in India. They make them feel less isolated in their new environment.
Unfortunately for Ashoke and Ashima, their children, Gogol and Sonia, don't feel quite the same way about their Bengali heritage. Much more assimilated than their parents into American society, they just don't have the same connection to the culture that has shaped their parents' whole outlook on life. They feel much more at home with American ways.
Yet the generation gap is by means insurmountable, as is proved when Gogol and Sonia find comfort in the old traditions in the wake of their father's death. In their establishing a reconnection with the old ways, the siblings are illustrating another of the book's themes: that in the final analysis, blood is thicker than water.