This rock carving at the World Heritage site at Vitlycke depicts a ship and a boat involved in what might be funerary ritual at sea. That naval vessels were important to the people of the northern Bronze Age is easy to see through the sheer abundance of ship carvings.
The ship seems to have had a prominent position in the Bronze Age view of life and death. Even though we don't fully understand what the ship symbolized, we can probably glean some of its meaning by looking at other cultures and mythologies, where our sources are less scarce.
In many cultures, the afterlife is reached through a sea or river voyage. This voyage of the dead tends to be a mirror image of the here and now, where the same things are important and the same orders are maintained.
Thus, the Egyptian pharaos, the divine keepers of the life-giving Nile, were transported to the next world in the same kind of boats that they used for their lavish Nile cruises while still alive.
In the maritime culture of ancient Greece, the deceased were expected to pay Charon the ferryman to be brought across the Styx - the river of death, to reach the afterlife.
In later Scandinavian tradition, for example during the Viking period, ship burials are well documented (for the time) and ship graves have been excavated at multiple sites.
Following this line of reasoning, it seems a safe bet that Bronze Age Scandinavians, being part of a maritime culture, had naval-themed burials, where the high and mighty were brought to the other side (either physically, metaphorically or spiritually) by naval vessels which were later immortalized on flat cliff surfaces near the waterfront were the burial ceremonies had been held. This mirrored the inequality in society, and the status of the new upper stratum, brought about by the luxury consumtion and long-distance trade typical for the Bronze Age, as well as the reliance on larger seafaring vessels that went hand in hand with this cultural shift.