Battling sin and its accompanying temptations is an internal battle. As much as the temptation might come from the outside of us, it is the inside of us where the battle takes place. Sin always occurs in the heart, before it manifests itself in our actions or behaviors. James 1:14 tells us this, "Each one is tempted when he is carried away and enticed by his own lust." Notice here that is is not someone else's lusts that we are battling against, but our own; it is not someone else's lusts that we are dealing with, but our own. This was Paul's point in Romans 7 as he talked about indwelling sin.
Unlike the old comedy skit by Flip Wilson, where he cried out, "The devil made me do it!"; we are complicit in our sin, because it starts and ends with us. The source of sin is within, within each one of us; and although we have been washed and made clean through regeneration, we still live in a body where sin lurks, and where it is all too ready to respond to temptation, all too ready to indulge its desires in both our flesh and our mind (Ephesians 2:3). James paints a graphic picture for us in 1:21 where he tells us that filthiness and wickedness still remain with us, as part of us.
What's the point? Be aware, be very aware of the ease with which we are tempted. Be aware, of how easy it is to sin. Be aware that we, as Christians, are still in a body of unredeemed flesh, in which filthiness and wickedness still remain. This is why Christ was chiding His apostles when they could not even fight their flesh to stay awake; and told them to watch and pray that they might not enter into temptation, because even though their spirit was willing, their flesh was weak. This is also why we are told in the Lord's prayer to pray to be led away from temptation and to pray that evil would not have its way with us.
So let us not be lulled to sleep, let us not be deceived, as sin is still crouching at the door desiring to master us; just as it has done from the beginning (Genesis 4:7). But let us be strong in the Lord, and the strength of his might, let us be watchful and praying, let us be ever diligent in awareness of our own weakness. Let us who stand, take heed lest we fall.