As Matthew describes the scene of Christ's death, there were not a few mockers present, deriding Jesus and calling out to him to take control of his fate:
Then two bandits were crucified with him, one on his right and one on his left. Those who passed by derided him, shaking their heads and saying, "You who would destroy the temple and build it in three days, save yourself! I you are the Son of God, come down from the cross." In the same way the chief priests also, along with the scribes and elders, were mocking him, saying, "He saved others; he cannot save himself. He is the King of Israel; let him come down from the cross now, and we will believe in him. He trusts in God; let God deliver him now, if he wants to; for he said, 'I am God's Son.' The bandits who were crucified with him also taunted him in the same way (Mt 27.38-44).
The passers-by and those surrounding Christ in his dying moments mocked him and his claims to be the Son of God: if he were really the Son of God, why doesn't he save himself? Come down off the cross!
In fact, however, Christ is the Son precisely because he is on the cross: he obeys the Father's commission to offer himself up for the sins of Israel and humanity, and thus is a true Son (cf. Rom 4.25, 8.3). This is the insight of Niko Kazantzakis's The Last Temptation of Christ: if Christ had come down from the cross -- just like Judas condemns the old man Jesus on his death bed as Jerusalem is in flames outside -- there would be no sacrifice for sins, no salvation, no redemption, and he would be no Son, since he had not obeyed the Father. At the end of the film, an old and dying Jesus crawls from his house into a desert, as Jerusalem is ablaze behind him, crying out, "I want to be the Son of God!" So also we find in Matthew that Jesus is the Son precisely because he obeys the Father's wish and will, in spite of the grave pains and struggles of his trial in Gethsemane (26.35-46).
An important lesson to draw from all this is: God doesn't think or evaluate things like man-in-the-flesh does. Here is another repeated point of the scriptures. The thinking, values, judgments, commitments, opinions, etc. of man-in-the-flesh are not like God's. The persons mocking Jesus considered death on a cross to be a fate worth evading at all costs, especially if the escape were available to someone like the Son of God. Because Jesus of Nazareth did not seek to escape it, he must evidently not have that power and thus must not be the Son of God. But the wisdom and goodness of God is shown in having power yet not using it (cf. 1 Cor 1.18ff.; Phil 2.6-11), in suffering for the sake of the very persons who nailed your hands to the cross. God's wisdom sees further than the pains of the moment into a glory far greater (cf. Rom 8.18; Heb 12.2).