Responsibilities in your Mind
1) Not Sleeping. To 'sleep' refers to becoming spiritually disengaged, indifferent or apathetic.
2) Keep Awake. This refers to being spiritually watchful so that you are able to see and prepare yourself for any spiritual dangers, temptations, and pitfalls.
3) Be Sober. This is just a good rule of thumb for life, but in this case, Paul is specifically warning us to make sure that we protect ourselves from anything that would dull our spiritual sensitivity and alertness.