The confession that the Holy Spirit is “person” … expresses primarily the experience that the Christian is not his own lord. Insofar as he lives out of faith in Christ, the center of his person that determines his behavior lies outside himself. The personal center of Christian action is the Holy Spirit
That the Spirit is the personal center of Christian action residing outside of the individual makes it understandable that in Paul, as elsewhere in primitive Christianity, the Spirit is characterized both as person distinguished from the Christians and also as a power that they possess internally. The Spirit comes to our aid (Rom. 8:26), gives witness to our spirit (v. 16), and claims our service (ch. 7:6); but he is also given to us, received by us, dwells in the believers, rests upon them. That both series of statements belong together is made clear by the insight that the Christian exists outside himself to the extent that he lives in faith in the resurrected Jesus and thus “in the Spirit.” The immanence of the Spirit in believers exists only through the fact that as believers they have found the ground of their life extra se, beyond themselves.
– Wolfhart Pannenberg, Jesus – God and Man, trans. L. L. Wilkins & D. A. Priebe (Philadelphia: The Westminster Press, 1968), 177.