A Christian runestone (notice the cross) at Fröberga (Frey's Mountain), Strängnäs municipality. The stone reads:
"Vighjälm and Ödmund raised this stone in memory of Sverker, their good brother."
Like most runestones on the Swedish east coast, the stone was raised during the very end of the Viking Age. The runecarver responsible for the inscription was (probably) a certain Balle, who was active during the 11th century and has made a great many of the runestones in the Mälardalen region.
Even if the runic alphabet entered old Norse culture somewhere around the second or third century CE, ancient Swedish/Geatish culture was by no means a culture centered on writing. Only a small elite knew the secret of the runes, as they had magical properties and their usage demanded care and mystical knowledge not bestowed on just any man (but as with all customs of the elite, the usage of runes did eventually spread to the lower strata of the population). This also meant that their usage differed from how Latin characters were used in Late Roman and Early Medieval Europe. These cultures can't be considered anything but oral either, but the written language permeated society in a way that was not the case in the north
The most striking example of this difference is the gradual appearance of a canonical text describing the exact meaning and interpretation of mythology - the Bible. The existence of this sacred tome centered on a single true God, almighty and benevolent (but harsh and strict), made it harder for alternative enterpretations and beliefs to take hold, and if they did so they were quickly, and often violently, stomped out. In comparison, ancient Norse religion, as well as most other polytheistic beliefs, is open to a multitude of interpretations to the point that these could be considered different religions. It also allows multiple, sometimes contradictory, stories of gods, monsters, good and evil, and with nuances between these extremes - gods are fallible and monsters are sometimes sympathetic. This also means that the myths can appear in different forms depending on who tells them and that the creation story in Völuspa doesn't necessarily harmonize with the one in Snorri's Younger Edda.