The NS records identify the name servers, responsible for your DNS zone. In order to have a valid DNS configuration, the NS records configured in the DNS zone must be exactly the same as those configured as name servers at your domain name provider. That way, resolvers will be redirected to the proper DNS servers, the same servers that are hosting your DNS zone.
Why do you need an NS record?
You need NS records because DNS queries respond with an authority section listing all the authoritative name servers. For that reason, it is mandatory for your DNS zone to have the proper NS records inside. Without NS records, your zone will stop working.