All the prophets - That is, the prophets in general. It may be said of the prophets generally, or of all of them, that they have foretold these things. This expression is not to be pressed as if we were to look for distinct predictions of the Messiah in each one of the prophets. The use of language does not require so strict an interpretation.
From Samuel - In the previous verse (22) Moses was mentioned as the first in order. The next in order was Samuel. The same mention of Moses and Samuel occurs in Psalms 99:6. The reason why Samuel is mentioned here is probably that he was the first prophet after Moses who recorded a prediction respecting the times of the Messiah. The Jews, in their divisions of the books of the Old Testament, reckoned the book of Joshua as the first of the prophets. But in Joshua and Judges there does not occur any distinct prediction of the Messiah. The prophecy in Samuel, to which Peter probably had reference, is in 2 Samuel 7:16. From the time of Moses to Samuel, also, it is probable that no prophet arose. God was consulted by Urim, and Thummim Exodus 28:30; Numbers 27:21, and consequently no extraordinary messenger was sent to instruct the nation.
As many as have spoken - Whosoever has declared the will of God. This is to be taken in a general sense. The meaning is, that the prophets had concurred in foretelling these days. They not merely concurred in foretelling a happy future period, but they foretold distinctly the very things which had actually occurred respecting Jesus of Nazareth; and the Jews, therefore, should listen to the voice of their own prophets.