The Dhammapada - 7 & 8

A person who lives contemplating on pleasant things,

who is not restrained in senses,

who does not know moderation in food,

who is indolent and of poor  effort,

Mara will overcome him,as wind a weak tree.

What is described here, is a recipe, how to become a prey of our own mind. For Mara, The Evil One, is not some outside force, some "devil" or deity of death and destruction, it is only our mind, our bad habits, laziness, evil intentions and especially ignorance, the true root of all evil. If we dwell with our minds only on the pleasant things, if we indulge in enjoying pleasurable things (subhānupassiṃ viharantaṃ), then it is easy for these tendencies in our brain ("Mara") to gain strength. The same thing happens, when we are unrestrained in six senses (eye, ear, nose, tongue, body and mind), taking in without restraint and reflection everything that comes and if we never have enough of sense pleasures (indriyesu asaṃvutaṃ). And of course, if we do not know moderation in food, we can expect the same result, because indulgence in food is actually a part of lack of restraint in senses (bhojanamhi cāmattaññuṃ). Laziness (kusītaṃ) and lack of effort to change our ways (hīnavīriyaṃ) will not help us to get rid of these bad habits and the roots of meditative life will slowly wither and die away. And without strong, often cultivated roots, the tree of our practice will not grow higher and higher, will never bring fruits in reaching the Nirvana, but our bad tendencies will subdue us, our hope for reaching the goal, just as easily, as wind uproots a weak tree.

The one, who does not live contemplating pleasant things,

who is well restrained in senses, 

Who does know moderation in food,

who is trusting and firm in effort, 

Mara will not overcome him, as wind a rocky mountain.

Here, on the other hand (in contrast to DhP 7) is described the way, how to nourish the roots of meditative life, how to destroy the bad tendencies, how to become immune to Mara, to the evil part of our mind. We must not dwell with our minds only on the pleasant things and indulge in enjoying pleasurable things (asubhānupassiṃ viharantaṃ). Another way to understand this phrase is that we should contemplate the unpleasant things, to understand that there is really nothing to be attached to, that attachment to pleasant things brings about the strength of "Mara", of our bad habits and tendencies. 

We must also be well restrained (indriyesu susaṃvutaṃ) in senses and know moderation in food (bhojanamhi ca mattaññuṃ). Thus, senses are guarded, we do not take everything in indiscriminately, and we contemplate on what we see, hear, smell, taste, touch and think. We are not attached to pleasant sense-impressions, we do not hate unpleasant sense-impressions, and we are observant and concentrated and thus able to bring meditation to everyday life. 

 Important part is also trust (saddhaṃ). Trust in the way, that the Buddha taught us, trust in the methods that are part of the way, trust in the goal that can be reached by following this way. Without this basic trust (which is not blind faith, for it is easily verified, as we go forward on the way) no progress is possible. 

We must also be firm in effort (āraddhavīriyaṃ). Effort is of course a basic necessity. We must make an effort to put everything that was said above into our daily lives. It is only by this constant effort, that we are able to progress towards the goal.

If we practice in this way, the roots of meditation will flourish, will become strong and invincible. Eventually, the tree of our practice will bear its fruit, our mind will reach the peaceful state of Nirvana. Mara, the dark side of our mind has no way to influence us, no way to overcome us, just like the wind is not able to blow away a rocky mountain.