A fantastically versatile card. While the restriction for one per deck is significant, it's the sort of card that can go into any deck and is never a bad card to see in your hand. Being neutral makes it easy to pay for and it can go on any hero, so there's no restriction on who can get one.
Providing an additional ready or healing for your defender can be crucial, and it can also provide resource acceleration if required as well. The threat increase is manageable if not used every turn, but can also be worked around with the myriad of threat control available in the full card pool. Trading the early threat for board state can be significant if drawing it early, even if it then becomes an emergency valve later in the game.
Pairs very well with Thurindir/Gather Information and Heed the Dream to find it quickly. Ideal targets are any hero defenders, but Erkenbrand is the one that stands out because he wants the healing more than any other. Favor of the Valar is a neutral way of ensuring you don't threat out while using it as well, so works very nicely together.
Also works very well for any Valour decks - can be used every turn for resource generation and help drive up your threat to get to 40 sooner, and can do it will more on the table through the extra resources as well.