Was the VOC a branch of the Dutch government, or was the Dutch government a branch of the VOC? The Dutch government was extremely trade-oriented during the 17th century, and the army would be deployed to protect the trade interests of the VOC.
Trade was indeed a big driver and the VoC basically was one of the first companies/multinationals that used the stock market to raise capital to build an enormous amount of ships that definitely had a lot of defensive/offensive capability. So the VoC was its own navy effectively. Ship building at the time was labor and capital intensive and required access to a lot of resources (e.g. timber). So capital and easy access to local trade routes (the rhine, baltics, etc.) was essential.
When these ships started bringing back goods from Africa and the Indian Ocean regions, people started making lots of money. Dominating the channel militarily and being able to deal with the French, Spanish, and British navies also was key. The scale of the VoC was simply unprecedented.