What does 'this' refer to in Acts 2:16?
In Acts 2:16, 'this' refers to the manifestation of the Holy Spirit coming down in a role completely different than He had ever played before. It points to the outpouring and visible work of the Spirit that the crowd was witnessing, which Peter identifies as that spoken by the prophet Joel.
Les explains that in Acts 2:16 Peter says, 'this is that which was spoken by the prophet Joel.' Les directs us to analyze what is the 'this' and what is the 'that.' The 'this' is the manifestation now of the coming down of the Holy Spirit, in a role completely different than He had ever played before. The Spirit has always been—He moved upon the face of the deep at creation, and David prayed, 'take not your spirit from me.' The Spirit has been evident, even though Orthodox Jews today do not like to recognize the Holy Spirit as a person of the Godhead, but Scripture does.
But this is that which was spoken by the prophet Joel;