the biggest mistake christians make is...
"Being too religious"!

What Is The BIGGEST Mistake Christian's Make?
Well obviously, this is a subjective opinion! Other folks may
believe that something else is a bigger mistake, but surely this one
fits up there pretty high on many people's list. My guess is
that many Christian's are making this very mistake and don't even
realize it! (And this is one of the reason's I think it is
the worst one!)
OK - here it is: I believe that the biggest mistake
Christian's make is that they tend to be too 'religious'!
"Huh?! Christianity is just another religion,
right? Therefore Christians are by definition religious!" you
might say. But let's think about that. The term
'religion' is hard to define...but let's try. Let's try from
a practical perspective - meaning what most people think of when they
hear the term. How about "the belief in a divine or
superhuman power or powers to be obeyed and worshipped as the
creator(s) and ruler(s) of the universe", or maybe "the practice of
religious observations and rites" (both from the Webster's New 20th
Century Dictionary, 1959). These are pretty close,
notwithstanding the debate regarding the applicability of 'non-deistic'
religions such as Buddhism or Atheism or Naturalism. In any
case, when most people think of the term 'religion', they think of the
belief in a supernatural being, and a list of do's and don'ts required
from that being.
And that is the problem. Most of the other religions fit this description, but true Christianity does not! Furthermore, when a Christian behaves like it does, he portrays an improper picture of the faith. Let me elaborate. All 'religions' have placed at the center of their universe either a God which must be appeased, or no God. We elaborate elsewhere why the 'no God' concept is irrational (something -indeed everything- from nothing, etc etc etc). Islam, Judaism, etc etc must do their good 'deeds' and await their 'judgment' from the divine 'judge'. They only rely on what they have either done or not done in their lives to live up to a supernatural standard. But Christianity is unique - contrary to popular opinion, it is totally opposite to this!
With Christianity, we don't have mankind trying to appease a God, or trying to be worthy of His love and mercy. In Christianity, the believer's don't attempt to be accepted by what they do - it is God who is reaching out to us! God loves us - unconditionally - and has extended His Grace to us, because of His mercy! Make no mistake, He is perfect, therefore He could never reconcile with anything less than perfect. We could NEVER achieve the perfection of God, which is required for reconciliation with Him. Our daily choices to ignore His sovereignty over all creation and place our wants and needs above Him separate us from Him. But He provided a way out - and He did it Himself, all we have to do is believe!
"But now a righteousness from God, apart from law, has been made known, to which the Law and the prophets testify. This righteousness from God comes through faith in Jesus Christ to all who believe...(all) are justified freely by His grace through the redemption that came by Christ Jesus." Romans 3:21-22a,24
What about all the 'thou shalts' and 'thou shalt not's'? We must remember that the Old Testament provides us the law - which when we see it shows us that we can never achieve this required perfection, as well as points to the redeemer of all who believe (indeed, even Abraham, the father of the Jews, was saved by 'faith', not by observing the law). The law shows us that we need a redeemer, and Christ is that fulfillment of the law for us.
"Therefore no one will be declared righteous in His sight by observing the law; rather, through the law we become conscious of sin." Romans 3:20
"Abraham believed God, and it was credited to him as righteousness."
Genesis 15:6
"The words 'it was credited to him' were written not for him alone, but also for us, to whom God will credit righteousness - for us who believe in Hi who raised Jesus our Lord from the dead. He was delivered over to death for our sins and was raised to life for our justification."
Romans 4:23-25
So why are some Christian's still requiring adherence to a list of
things a person should or should not do? It is a case of
misunderstood timing. We see now that we are only saved by
our trust in Jesus to present us acceptable to God (this is what
'faith' is), and when we understand the love He showed to us, and the
things He went through for us (His perfect life, and His death), we are
overcome with gratitude. He is our Savior, and therefore He
has earned the right to be our Lord. So what do we do for our
Lord? We obey Him.
"Therefore, I urge you brothers, in view of God's mercy, to offer your bodies as living sacrifices, holy and pleasing to God - this is your spiritual act of worship. Do not conform any longer to the pattern of this world [which is self-centeredness], but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is - His good, pleasing and perfect will." Romans 12:1-2
You see, we obey because we love Him back, and are thankful.
We don't obey in order to be saved, but we can see how healthy our
faith is by our actions.
"What good is it brothers, if a man claims to have faith but has no deeds? Can such a [counterfeit] faith save him? ...faith without deeds is useless [it is a dead faith].
James 2:14,20b
So, the problem comes when a Christian projects the fruits of faith
onto a person who has no faith. This confuses the
non-believer, and causes him to think that he must accomplish all these
things (or not do all these others) in order to be saved. It
causes a misconception about 'fun' or 'boring', by thinking that the
Christian must legalistically limit 'fun things' and only allow 'boring
things'. When instead, after the Holy Spirit has renewed the
believer's thinking and created a 'new life' in Christ, our whole
perspective of 'fun' and 'boring' changes, due to gratitude and
Lordship. The end result of this bad perspective usually does
nothing to bring the non-believer to a thinking condition about the
faith, and instead just 'turns them off to it', which is a
tragedy. A Christian should appropriately model a loving,
caring, and long-term thinking lifestyle, and point the non-believer to
the evidence external to him (in the world) as well as internal (inside
the non-believer). We assist the Spirit in the conversion
process, and then leave the fruits of the faith to be worked out
between the new believer and his Savior and Lord. Then and
only then is it appropriate to assist in spiritual growth, provide
accountability, or rebuke a believer according to his deeds.
The bottom line of this problem is that the Christian can sometimes provide the wrong picture of Christianity to the non-believer by his actions. And if this sends the non-believer away with a bad taste in his mouth, then the Christian has committed a terrible mistake.