Hi, yes the purpose of a loopback interface is to keep your vlan interface always Up. It can be a good thing, but can also turn out to be a bad idea, depending on the topology and use case. If your router is keeping advertising the route to a resource it can't reach anymore, that's not necessarily a good idea.
As correctly stated previously, for your vlan interface to be Up, you need at least one active port in it, and enable ipforwarding for that vlan as well. Then routing can happen with other vlans with ipforwarding also enabled. This is also a prerequisite to configure any dynamic routing protocol, like OSPF.