Acts 3: 20 And he shall send Jesus Christ, which before was preached unto you:

21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.

The times of restitution of all things] The Greek word used here means to establish or settle anything. It is simply talking of the restoration of something that was once in a good state, but went bad, to be restored back to its original good state, it is a change from a bad state to that of a good state, that it has originally.

.For example, when in Acts 1:6, when the disciples asked ‘Christ, Wilt thou at this time restore again (apokayistaneiv) the kingdom to Israel?’ It was simply will you take the kingdom from the Romans and give back to the Jews? As it were the original owners of the kingdom.

Now, this restoration is connected to that “which God hath spoken by the mouth of all his holy prophets”, it therefore means all the prophecies and promises as contained in the Old Testament relative to the kingdom of Christ upon the Earth