Peter in Acts 5 teaching of the Lord's ministry and his purpose:
"God exalted him to his own right hand as Prince and Savior that he might bring Israel to repentance and forgive their sins."
The Lord's ministry was to "confirm the promises made to the [Hebrew] fathers" (Rom 15:8). The Acts age was a continuation of the call for Israel to repent (as Peter preaches post-Pentecost in Acts 3 and 5). If she had, the kingdom of heaven would have come in then (it was "at hand").
"Now, fellow Israelites... Repent, then, and turn to God, so that your sins may be wiped out, that times of refreshing may come from the Lord, and that he may send the Messiah, who has been appointed for you—even Jesus. Heaven must receive him until the time comes for God to restore everything, as he promised long ago through his holy prophets." (Acts 3)
This was not an empty promise. The "times of refreshing" for Israel would have come had national Israel repented.
Remember, the one question they had after enlightenment by the Holy Spirit and after 40 days of the resurrected Lord personally instructing them:
Then they gathered around him and asked him, “Lord, are you at this time going to restore the kingdom to Israel?” (Acts 1:6)
This is the context that will help us understand not only the parables of Matthew, but also the Book of Acts and its epistles as well.