In a first instance divine shifts are defined however the players and GM negotiate. The reason for this is to allow a high level of customisation to the godly powers the players wield. I gave a lightning god a divine shift that conferred a lightning damage bonus to all attacks made using a dagger throwing ability they had following the rules for a Single attack shift Page 142.
But in the example you give, a Strength shift is actually defined also on Page 142. as an asset on all Strength checks excluding attacks as well as some extra damage. So actually in this case the definition is very narrow.
Strength: All tasks involving strength, including jumping and dealing
damage in melee or thrown attacks (3 additional points of damage per
shift) but not attack rolls
A divine shift in Accuracy confers an asset on all attack rolls though. Combining these two is a common trend in the more martial gods I've GM'd.
All that said divine shifts are incredibly powerful which is why they are locked behind the divine labour tasks and obligations also detailed on Page 142.
Shifts can also only ever be stacked three times. So three divine shifts in Strength would ease the difficulty of strength test outside of attacks by 3 steps and confer a total bonus of 9 damage on successful attacks.