“Keep watching and praying that you may not come into temptation; the spirit is willing, but the flesh is weak.”” (Mark 14:38, NASB95)

Jesus to Peter, James, and John in the garden on the night that he was betrayed.  He understood what was coming, the disciples could not stay awake.

Certainly they wanted to stay awake, because Jesus was awake and praying and it wouldn’t look good for them to be sleeping while he was praying.  The spirit was willing…

…But the flesh was weak.  Try as they might, they could not stay awake and they were rebuked by Christ for falling asleep.  A humbling incident, especially looking back in light of what would happen to Christ that night, at the time of his greatest need, they first fell asleep on him, and then abandoned him.  One has to love the honesty of the disciples here and willingness to expose themselves to shame by recording the incident.

Augustine quotes this verse and then comments:

Such prayer is indeed in itself an admonition to you that you need the help of the Lord, and that you ought not to rest upon yourself your hope of living well. For now you pray, not that you may obtain the riches and honours of this present world, or any unsubstantial human possession, but that you may not enter into temptation, a thing which would not be asked in prayer if a man could accomplish it for himself by his own will.

Prayer is necessary just because the flesh is so weak.