Barcelona needs to try their best in order for them to win Osasuna, otherwise, they'll have to fight till the end of the season on pressure to make sure Madrid does not take over them. I feel this is the best opportunity for Barcelona to widen the point gap, because we don't know the unforeseen challenges that might come up in future before the end of the season. It's an important match for Barcelona.
It is indeed important for Barcelona because every opportunity is a good opportunity for them so Barcelona must be able to win the match with Osasuna. Because it is their chance to establish themselves at the top of the standings until the end of the season even though Real Madrid will still follow them in second place but that will not be dangerous enough for Barcelona as long as the points gap is still there for capital to stay at the top of the standings.