Preheat your oven to 350°F (175°C) and grease the 9x13 inch baking pan or line it with parchment paper for easy removal.
In a medium bowl, whisk together the flour, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar together until creamy and well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the flour mixture to the wet ingredients, mixing until just combined.
Fold in the rolled oats and raisins until evenly distributed throughout the batter.
Spread the batter evenly into the prepared baking pan, smoothing the top with a spatula.
Bake in the preheated oven for about 25 minutes, or until the edges are golden brown, and a toothpick inserted in the center comes out clean.
Allow the bars to cool in the pan for 10 minutes, then lift them out using the parchment paper (if using) or cut directly in the pan. Let them cool completely on a wire rack before cutting into 12 equal bars.