"Look at what you sent forward for tomorrow"

أَيُّہَا ٱلَّذِينَ ءَامَنُواْ ٱتَّقُواْ ٱللَّهَ وَلۡتَنظُرۡ نَفۡسٌ۬ مَّا قَدَّمَتۡ لِغَدٍ۬‌ۖ وَٱتَّقُواْ ٱللَّهَ‌ۚ إِنَّ ٱللَّهَ خَبِيرُۢ بِمَا تَعۡمَلُونَ

"O you who believe! Fear Allah and keep your duty to Him. And let every person look to what he has sent forth for the morrow, and fear Allah. Verily, Allah is All-Aware of what you do."

(Qur'an 59:18)

"O you who believe! Fear Allah" ordains the Taqwa of Allah which pertains to obeying what He ordered and staying away from what He forbade.

"and let every person look to what he has sent forth for tomorrow," meaning, hold yourselves accountable before you are recompensed, and think deeply about what you have kept for yourselves of good deeds for the Day of your return and being paraded before your Lord,

"Fear Allah" again ordering Taqwa,

"Verily, Allah is All-Aware of what you do." Allah asserts that surely, He knows all of your deeds and actions. Nothing that pertains to you ever escapes His observation, nor any matter of yours, whether major or minor, is ever beyond His knowledge

(Tafsir Ibn Kathir www.tasir.com)