Our Scripture reading today is Hebrews 5:12-14.
Verse 14, "But strong meat belongeth to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil."
As we grow in our walk with the Lord, it will strengthen our spiritual senses.  It is of the utmost importance that we see spiritual growth.  Let's just say we would think something is not right if we saw a 21 year old young man drinking from a sippy cup or even a baby bottle.  It is not normal.  Think about the fact that a baby or even a small child will put anything in their mouth.  If it will fit, it is going in.  They cannot discern the paper clip they found on the floor is not a piece of candy.
The same can be said of Christians who are not growing their daily life.  Their level of spiritual discernment has not been exercised enough.  We all need greater spiritual discernment.  The devil is the master deceiver.  He can make something look really good, but using spiritual discernment we can steer clear of whatever he was leading us to do.
Ephesians 1:18, "The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,"
Revelation 2:7, "He that hath an ear, let him hear what the Spirit saith unto the churches; To him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God."
God has given us His Spirit, His Word and His church.  Each one of these are meant to increase our spiritual discernment. All 3 are important and must not be neglected.