Because strait is the gate, and narrow is the way, which leadeth unto life,
and few there be that find it.
The word used for life in that verse is zoe, which refers to the highest form of blessing a human being can have in the Spirit.
Furthermore, Ephesians 1,3 says that YOU were already blessed with every spiritual blessing in heavenly places. Now it is up to you though, to call those blessings into your life, right here and now!
Your inner man (your Spirit) is already blessed with every spiritual blessing, but as long as you only live by your outer man (your flesh/body), you will never be able to have those spiritual blessings manifest in the physical realm.
That means that you have to live from the inside out, instead of from the outside in! (Instead of letting your circumstances control you, you control your circumstances through your Spirit - from the inside out.)
So how can I live from the inside out?
God says, that His WHOLE kingdom works by the principle of sowing and reaping, and that is also the principle in this situation.
You have every spiritual blessing at your disposal, which means that you can call those blessings from the heaven to the earth and change your circumstances into heaven on earth.
So if you sow that seed of a spiritual blessing, which is already in your Spirit man, into your life, then you can reap the fruits of the blessing in your body and in your circumstances. (From the inside out. Like a seed.)
So take the word of God (the good seed) and sow the blessing that He gave to you in midst of your problems and your circumstances. Then you won't have to eat the rotten fruit of this world any longer, but can reap fruits of the Spirit. Fruits of heaven.
BE the man that understood and practices the principle of sowing and reaping in their life and thereby enters into the strait gate that leads to the highest form of blessing a human being can experience, right here and now!
As christian, you are not to be an outside-in kind of person, but you should live from the inside-out!
Your inside man (Spirit) is blessed with everything you could ever need or want. It has Gods abundance and all of His power, but as long as you let your outside man (body) control you, your Spirit man cannot take the upper hand.
Live from the inside out and start letting your Spirit man take authority over your body and all your circumstances. That’s how you will live the way you ought to and receive what you have been waiting for! (Ephesians 1,3 & Matthew 7,12-14)