Acts 1:7

And he said unto them, It is not for you to know times or seasons, which the Father hath set within his own authority.

The kingdom in its present phase would begin very shortly; but Jesus passed over their ignorance on that point, fully aware that with the coming of the Spirit upon them they would have it brought to their remembrance all that Jesus had already taught on that question; but human curiosity is unlimited, and Jesus immediately warned his apostles that the final phase of the kingdom, including the resurrection and final judgment, would come at a time unknown to any man, not even to himself in his earthly limitation.

Bruce called this:

The last flicker of their former burning expectation of an imminent political theocracy with themselves as its chief executives. From this time forth, they devoted themselves to the proclamation and service of God's spiritual kingdom.[10]

Those interpreters who hold to the future conversion theory regarding Israel usually assert their conviction as related to these verses, as for example, Harrison: "This does not mean that God is through with Israel; Romans 11:26 says that all Israel shall be saved."[11] However, the "Israel" in view there is spiritual Israel, not the hardened secular Israel. There is no New Testament teaching to the effect that secular Israel will accept Jesus Christ; but, on the other hand, it is indicated that they will remain hardened "until the fullness of the Gentiles be come in" (Romans 11:25), a time that may coincide with the coming of the end of the world. The future conversion of secular Israel is neither affirmed in Scripture nor denied as possible.

[10] F. F. Bruce, op. cit., p. 38.

[11] Everett F. Harrison, Wycliffe Bible Commentary (Chicago: Moody Press, 1971), p. 385.