In this passage, Fee comments on 2 Corinthians 1:21–22, "But it is God who establishes us together with you in Christ and who anointed us, who also sealed us and gave us the Spirit in our hearts as a down payment." (NET)
The metaphors in this text also demonstrate in striking ways that the Spirit for Paul is principally an eschatological reality. The presence of the Spirit as God's seal and down payment is the unmistakeable evidence of salvation as 'already but not yet.' The future is already in evidence through the 'down payment,' the present guarantee; but he is present only as 'down payment': the final inheritance, which he guarantees, is yet to be realized. (294)
Fee describes the experience of the Spirit in "Already but Not Yet" terms. The Holy Spirit is the very presence of God in the believer today--it is the primary way that we experience the eschaton. However, the Holy Spirit is not present in the complete way that He will be in the eschaton. It is a real presence, but not a complete presence.