I have found that the main reason Christians will find it hard to stay faithful is that we live in a world that has an allure and its constantly calling us to give in to our fleshly natures. Its a battle and is hard to keep the faith. After all you are having to forgo what may seem more easier and comfortable to do. Its hard to store up your riches in heaven and not go for the glitter of whats right in front of you. Especially nowadays where the world has become even more about self and there are more comforts. But all that glitters is not gold and what looks like something that will give you a better life and make you more happier will end up letting you down in the end.
I know its hard to hang in there and not be swayed by the constant noise of people saying that believing in God is illogical and unreal. They will keep attacking you and it may seem like on the surface what they are saying makes more sense. But this world is only a temporary thing and all that is presented will fade away. The road to sin is wide and easy but the path to follow God is narrow and against what looks good in this world. But you have to see beyond all that and trust in God and He will come good in the end. You will find what is the true key to life and it will give you an abundance of peace and joy knowing that you are a child of God and He will look after you forever.
Matthew 6:19 - 20
19"Do not store up for yourselves treasures on earth, where moth and rust destroy, and where thieves break in and steal.
20"But store up for yourselves treasures in heaven, where neither moth nor rust destroys, and where thieves do not break in or steal;
21for where your treasure is, there your heart will be also.