أَكَادُ أُخْفِيهَا (I would keep it secret - Ta-Ha 20:15 ⧉): Allah Ta` ala says that He wishes to keep the circumstances relating to the Day of Judgment hidden from all created things including prophets and angels. The word أَكَادُ (I would) gives a subtle hint that it is only to induce people to good deeds that the coming of the Day of Judgment has been disclosed, otherwise even this fact would have been concealed.
لِتُجْزَىٰ كُلُّ نَفْسٍ بِمَا تَسْعَىٰ (So that everyone is given a return for the effort one makes - Ta-Ha 20:15 ⧉). If this phrase is taken to be linked with the word آتِيَةٌ (has to come) then it would mean that this world is not a place of requital. Here a person does not receive recompense according to his merits and even if he receives some reward in this world it is just a token which does not constitute the full recompense of his deeds. It is, therefore, essential that there should be a time when everybody would receive his due reward.
Another possibility about the construction of this phrase is that it is taken to be linked with the words أَكَادُ أُخْفِيهَا (I would keep it secret - Ta-Ha 20:15 ⧉). In this case, it would mean that the philosophy in not revealing the time of death and the Day of Judgment is that people should continue in their endeavours and should not cease to strive in the belief that their own death or the Day of Judgment are still far away in the future. (Ruh)