Could you cast runes, not just to predict the future, but to manipulate it? Actually, they were not usually cast to predict the future. It can be cast for that purpose. It’s not invalid. It just wasn’t their most common focus.
It was thought that your future was dictated by your personal luck. We get the word luck from them. But in the original sense, luck was a force more like karma than like random good fortune as we think of it today. Luck was coupled with the concept of wyrd from which we get both the word weird and word itself. The three fates were also called the wyrd systers or word sisters.
You cast them to gain insight into something of the present? To aid your luck perhaps? Yes, exactly. It was thought that by having the proper runes craft into your tools and clothing, you could balance the influence of your luck, but you could never really defy your wyrd.
Balance your spirit with a symbol? Well, balance your karma with a symbol.
Like adding some crit points on your sword. Indeed. The spirit was your wyrd. Your luck was considered independent of your wyrd. The village priest might have been seen as a good man, might have been genuinely liked, but it was believed that to take a Christian priest out to sea was bad luck. It would cause storms. They came to this conclusion from the Christian story of Jonah and the whale.
They used the runes more as a balancing tool then for divination? Yes, and a way of communicating with the world itself. But it all started with the wyrd. Because of your wyrd you might be destined to be a shaman or a warrior, a trader or a skald. Your wyrd might set you up to be a warrior, but you might still carry around bad luck as well, where other warriors would have better. So the impact of chants was to add or remove an influence on your luck.
Do we know when the rune casting for divination got started? Later, with the rise of Roman dominance, the concept of sortilege was sort of cross fertilized by what they witnessed of Latin sorcery. It was really popular in Roman political circles, and is actually the origin of the concept of a court wizard. It is also roughly where we get the concept of a vizier from.
Your thoughts are welcome. Be well friends.