since its from the Halo 2 soundtrack its a fairly easy analogy to connect this to the partnership formed between the Master Cheif and the Arbiter. It could also be Master Chief and Cortana since the two of them help each other out more often than the Cheif and the Arbiter do.
On a more general note, it's about a relationship, being there for each other. Take it further than that as needed by you but in simplest terms, it's about being there for someone who is very close to you.
since its from the Halo 2 soundtrack its a fairly easy analogy to connect this to the partnership formed between the Master Cheif and the Arbiter. It could also be Master Chief and Cortana since the two of them help each other out more often than the Cheif and the Arbiter do.
On a more general note, it's about a relationship, being there for each other. Take it further than that as needed by you but in simplest terms, it's about being there for someone who is very close to you.