Stephen gives a long speech before the Temple officials and priests which spans chapter 7 of Acts. His discourse covers the history of the people of Israel, from the calling of Abraham to the Exodus from Egypt, to the conquest of Canaan, to the building of the Temple.
In many cases it is plain the details he mentions are a part of his polemics against the Temple officials who refused to believe in Christ. For instance, when he says that Moses presumed the Israelites would understand that he had come to save them but instead was rejected (vv. 23-9), there is a clear parallel to Christ, who came healing and doing good to all only to find himself crucified in the end. Likewise when he cites Moses' words that "God will raise up for you a prophet like me from your own people" (v. 37), it is plausible enough that he intended them to understand that Jesus of Nazareth was precisely this prophet.
But Stephen's speech ends on a strange note. At the close of his retelling of the history of Israel, before he engages in some direct polemics against the "stiff-necked" priests (v. 51), he mentions David, Solomon, and the building of the Temple. But afterwards he is sure to note that "the Most High does not live in houses made by human hands" (v.48). Why mention this? What is the connection to Christ?
Like I've noted before, a central point of contention between Jesus and his followers, on the one hand, and the Judean authorities, on the other, was the status of the Temple. Jesus considered the Temple corrupt and foretold its destruction (which would eventually be realized by the Romans in 70 C.E.). Jesus regularly offered himself as a sort of alternative to the Temple, healing and forgiving sins (consider the episode at Mark 2.1-12, for instance) much to the consternation of the Pharisees, Sadducees, and other religious groups. God himself apparently makes appearances and works deliverance outside of the Temple, and this to the jealousy of the Temple officials themselves (5.17).
Stephen possibly stresses that God is not contained within the Temple for this reason: to verify, citing from Isaiah 66, that God is more than capable of being active outside of the Temple context; and evidence of this is the clear working of miracles through Christ, both during his earthly mission and now through his disciples. If God is not contained in the Temple, then this objection to the legitimacy of Jesus of Nazareth as Christ -- namely, that he was rejected by the Temple authorities (cf. the Pharisees' remarks at John 7.47-9) -- cannot be valid. If God is contained in the Temple, then there is no impossibility in his being present and active in someone outside the Temple system.