Maryam 19:21 states: وَلِنَجْعَلَهُ آيَةً لِلنَّاسِ وَرَحْمَةً مِنَّا وَكَانَ أَمْرًا مَقْضِيًّا
“So that We may make him a sign for people and a mercy from Us; the matter has been decreed.”
Āl ʿImrān develops the account of Jesus’ mission and signs in greater detail. Reading the passages together shows how different surahs may supply complementary aspects of a single subject.
Benefit: the fuller passage can clarify the briefer one, but a suggested syntactic ellipsis remains an interpretive proposal and must not be confused with revealed wording.