How to solve the problem of saving multiple entities?

Question

Doctrine ORM

Please tell me what is the difference between the 2 codes:
1)

public function setSave()
    {
        $this->entityManager->flush();
    }

2)

public function setSave2(EntityMS $entityMS)
    {
        $this->entityManager->merge($entityMS);
        $this->entityManager->flush();
        $this->entityManager->clear();
    }

save problem why code 2 handles better than the first one.

I am storing three entities in a repository function. I don't understand why the first code doesn't work, the second one does.