Acts 7:17

But when the time of the promise drew nigh, which God had sworn to Abraham, the people grew and multiplied in Egypt,

But when the time of the promise drew nigh belongs to Stephen's defense before the council in answer to the charge of blasphemy. It was spoken in a clear, thrilling voice that held the assembly spellbound. In it he rehearses the history of God's chosen people, beginning with Abraham and tracing generation to generation in the national records of Israel down to Solomon, taking up the most impressive points to vindicate his cause. The utterance shows thorough knowledge of the Jewish economy and its spiritual interpretation now made manifest through Christ.

It is part of Stephen's testimony preaching Christ from the Old Testament Scriptures, beginning with Moses and the prophets. It presents the Scriptures as testifying of Christ. It produces evidence for Christ, giving inspired proof of his mission, suffering, death, resurrection, and ascension, and so proves the identity of Jesus with the Messiah through the testimony of Moses and the prophets. It shows that the voice of Christ spoke through the prophets and patriarchs from the days of Adam to that time. It shows that Christ is the key unlocking the Old Testament and giving access to its riches.