Why does Odin favour Sigi at the beginning of the Saga of the Völsungs?

Question

In the beginning of the Saga of the Völsungs, we learn of the senseless murder of the thrall Bredi at the hands of Sigi. Although Sigi is condemned and declared a "wolf in holy places" (an outlaw), Odin helps him attain warships and troops and he eventually becomes a great king.

Thus it is well seen that Sigi has slain the thrall and murdered him; so he is given forth to be a wolf in holy places, and may no more abide in the land with his father; therewith Odin bare him fellowship from the land, so long a way, that right long it was, and made no stay till he brought him to certain war-ships. So Sigi falls to lying out a-warring with the strength that his father gave him or ever they parted; and happy was he in his warring, and ever prevailed, till he brought it about that he won by his wars land and lordship at the last; and thereupon he took to him a noble wife, and became a great and mighty king, and ruled over the land of the Huns, and was the greatest of warriors. He had a son by his wife, who was called Refit, who grew up in his father's house, and soon became great of growth, and shapely.

_{Source: The Story of the Volsungs, translated by William Morris and Eirikr Magnusson}

I understand that Sigi supposedly is a "son of Odin", however it doesn't seem quite right that the Allfather would favour him as much after he is identified as a murderer.

Is there an explanation for Odin's morally questionable preference of Sigi?

Answer 1

One has to remember that the northern mythology is not based on morality (like Abrahamic religion) and interactions between gods and men (like those in Greek myths) are rare; Odins interest in the world of men is not to promote "good" behavior, it is to harvest strong warriors that will ultimately fight for him in Ragnarök. For Odin, it is better if Sigi is not killed as an outlaw and goes to Hel, but rather becomes a warlord that goes on a rampage which causes many men to die in battle, and that also can father sons which also will become strong warriors.

This fundamental attitude of Odin is reflected in several of his alternate names that means something like "deceitful": he might favour you for a while, but eventually, that favour will end and you will be dead.

Answer 2

I'm no expert in the Völsungs, but my overall sense from the body of the sagas is that killing is not necessarily a capital crime (blood money and the ostracism of outlaw status as opposed to execution.) Many of the heroes of the sagas will commit seemingly random, senseless acts of violence (although there is usually an insult or slight that incites it, either real or imagined.) Generally it's a turning point in some part of the story arc that drives the narrative, either through exile or a feud or some other consequence. Many of the heroes evinced quite poor behavior early in their lives—Grettir and Egil come to mind as paragons. One of the elements I like most about the later sagas in particular is the depth of character development over the course of the heroes' lives as they mature and wizen and gain some kind of redemption.

Thralls did have some protection, but they were essentially slaves and thus regarded as property, so I wouldn't think killing one, even if unjustified would be regarded as an unforgivable offense, especially by Odin, god of war and beloved of the ruling class.