إِنَّمَآ أَمْوَٰلُكُمْ وَأَوْلَـٰدُكُمْ فِتْنَةٌ ۚ وَٱللَّهُ عِندَهُۥٓ أَجْرٌ عَظِيمٌ
Innamaa amwaalukum wa awlaadukum fitnah; wallaahu 'indahooo ajrun 'azeem
Your wealth and your children are only a trial, and with God is a great reward.
Placed straight after a verse about conflict inside the household that ends by urging pardon, this puts the whole relationship under test. Fitna carries both the testing and the pull that makes something hard to release, so wealth and children are named as what a person most wants, which is exactly why they measure anything. The reward clause arrives in the same breath and keeps the sentence from landing as a warning alone.