What Are the Firstfruits of the Spirit?

As mentioned in the introductory article on firstfruits, one of the New Testament uses of the concept of firstfruits is found in Romans 8:23, which says

Romans 8:22-23
For we know that the whole creation groans and labors with birth pangs together until now. Not only that, but we also who have the firstfruits of the Spirit, even we groan within ourselves, eagerly waiting for the adoption, the redemption of our body.

What are these firstfruits of the Spirit? I am aware of two common explanations (feel free to comment if you have another view!):

1. That believers in this present age are the first people to receive the Spirit of God, and, in that sense, represent the "firstfruits" of those who will receive the Spirit.
2. That the measure of the Spirit given to believers in this present age is only a small portion of what God intends - i.e., individuals currently have the "firstfruits of the Spirit" in their lives but will receive the fullness of the Spirit at the resurrection.

If you had asked me a few weeks ago what I thought the "firstfruits of the Spirit" were, I would probably have said something along the lines of view #1. When I came across view #2, it also seemed to make sense. After some analysis, I don't think either of them accurately describe what is being said in Romans 8:23.