Hi BT,
If we look at the first 10 chapters of Acts, whether it was supposed to be a Jewish ministry or not, It clearly was....
The question is, If we believe Gentiles should have been let in, then Peter was clearly wrong. OR, the offer of grace given to Israel (a second chance) was the beginning of "the dispensation of grace" BUT also the beginning of a transition to a calling apart from the nation of Israel (the One New Man)... God knew they would fall at Acts 28, so He made provisions accordingly (fitly framed)
that does not mean the offer of the Kingdom was not valid. What happened during Acts was the door was opened to the Gentiles so when God picks up his plan during the Tribulation, Gentiles will still be invited to the wedding.
The Kingdom was "at hand" in the Gospels because the King was there and was going to sacrifice Himself for the sins of ALL... The kingdom could not actually be offered prior to the events of Calvary... thus sayeth the scriptures.
Peter was now offering the kingdom in the first part of Acts. - the first few speeches confirm this.
Act 10:36-37 KJV
(36) The word which God sent unto the children of Israel, preaching peace by Jesus Christ: (he is Lord of all
(37) That word, I say, ye know, which was published throughout all Judaea, and began from Galilee, after the baptism which John preached;
And when Peter uses the keys to the Kingdom of Heaven to let Gentiles in, He states the word has not changed since the baptism which John preached (which was sent to Israel).
I believe there was Two Witnesses running around during acts, just like there will be during the Tribulation
.
Heres a great summary of Acts written by my Pastor. - Lesson 1 explains the above much better...
http://www.opendoorbaptist.com/articles/actslssn.html