"Watch and pray that you may not enter into temptation," encouraged Jesus. Matthew 26.41
Even Jesus' disciples could not keep the standard of alertness and faith Jesus asked of them. They felt sleepy, and therefore did not pray or keep alert, though they should have.
The world weighs us down, thoughts stir and trouble us, we are constantly being drawn away from God by simply living in the world and contact with the worldly.
Many times I should be heeding the same advice Jesus gave his disciples but either I am too tired or drawn away from faith. But a lot of times when I feel temptation offered, I do stay awake and pray, and God helps me overcome. Or maybe sometimes my faith is so blocked that I can't honestly discern Gods guidance at the time.
Perhaps Jesus also wanted us to prevent temptation in our futures, and watching and praying will pre-empt any temptation aimed at us. Therefore when it comes we are prepared and will be able to overcome.
A soldier on sentry duty watches. He is alert, all senses on and prepared to react to an adversary. He stays on watch till his commander deems it safe enough to stand down. It is the same with us. Or should be.
Jesus advised us to watch. That means to stay alert. And to pray as well. Watching and praying can mean staying awake all night in prayer, praise, etc. Luke 6.12 says Jesus prayed all night to God. Sometimes God might want us to spend an extra hour with Him, watching by reading the Bible or uttering some prayer or another.
Watch and pray that and so that you won't fall into temptation.