"Keep alert and pray. Otherwise temptation will overpower you. For though the spirit is willing enough, the body [the flesh] is weak." (Matthew 26:41)
For me, this verse ties in with yesterday's verse about being faithful. There is always the temptation to do something other than what we should! The temptation to be complacent or lazy, procrastinating. The temptation to complain, to be ungrateful. The temptation to be selfish. The temptation to live for entertaining ourselves (especially by viewing things that are not edifying and glorifying to God—not just porn, but media that promotes anything ungodly—gossip, materialism, impure actions, immodest dress, violence, etc.). Etc. Etc. Etc.
I love what the Life Application Bible Commentary says about this verse:
"Jesus used Peter's drowsiness to warn him to be spiritually vigilant against the temptation he would soon face. The way to overcome temptation is to stay alert and pray. This means being aware of the possibilities of temptation, sensitive to the subtleties, and resolved to fight courageously. Because temptation strikes where we are most vulnerable, we can't resist alone. Prayer is essential because God's strength can shore up our defenses and defeat Satan."
To me this shouts: KEEP YOUR HEAD IN THE GAME! You can't afford to doze off spiritually. You've gotta be checking in with God all the time—and relying on His strength to do what you should.