A prophecy given to Daniel back in the third or second early century B.C. came to fruition in 31 A.D., hundreds of years later. The mathematical possibilities of just one prophecy of this nature alone coming true would take an impossibly small probability to happen in reality.
Therefore, the first 69 weeks strengthen the reason to believe in Christ’s death, resurrection, and plan of salvation for our lives. He fulfilled the impossible.
But the weeks also matter historically. Daniel, and his people, had endured a great deal of tribulation, leading up to and after Jesus’ death and resurrection on the cross. Babylonians had destroyed Jerusalem and taken many people captive. The Seleucid Empire attempted to force the Israelites to conform to Hellenistic culture, which lead to the Maccabean revolt (celebrated in the holiday of Hanukah). Romans overtook Israel and, later, destroyed the temple and scattered the Jewish people in an event known as the diaspora.
They needed something to hope in. They knew when they reached the end of the 70 weeks that everlasting righteousness was in sight (Daniel 9:24).
It matters for Christians today, too.