Man is not promised an endless supply of strength for him to store up. Rather, God promises to provide the necessary grace and strength for the present trials.
Change often results in fear. As such, it must be met with strength. Failure to do so can breed panic that only God's strength can overcome.
Many people use time set aside for rest to do things that deprive of rest. This compounds the need for rest and the problems associated with not getting any.
At times, God called people to enter into war with the goal of killing their enemies. The Bible clearly distinguishes between this type of killing and murder.
