Section 1 Introduction

Jesus said that by a persons’ (spiritual) fruit you would know them as either belonging to Him or to Satan. The mark of any true practicing Christian is their love for Jesus and its expression to others.
What faith would you follow? One that expresses the Love of Jesus? Or one that expounds theology and knowledge?  Catholic and Protestants are very similar in the expression of their life style when Jesus is lord of their life.  Be careful judging the salvation of another, regardless of what denomination they are until your obedience is fulfilled as you may find they love Jesus more than you and that you are found wanting in expressing the Love of God in the way they do!
Where the Bible clearly shows their beliefs are wrong then you are to point to The Bible as their judge. But you are still not able to judge or condemn them as that is the prerogative of God alone. It is His Bible and He alone is to judge people in accordance with it.  All you can do is humbly point them to what it says and then let God deal with them.
In theory Catholic and Protestantism should not be much different as they both follow the same Greek Text and use the same or similar Bibles.
Why the differences then?
It is because tradition and denominational approach affect the way Bibles are translated or interpreted  and the way it is interpreted results in their belief system, and the way a person expresses Jesus in their life!
Attitudes in a denomination that deliberately reject, misinterpret or compromise what the Bible states or teaches are in purposeful disobedience to it, will be in error and this error will be taught to their adherents.  It is their mistranslation or rejection of Bible truths that cause the problems ecumenism tries to resolve but cannot really resolve if a true Biblical approach is taken to it.
All that is required to solve the problem of ecumenism is to obey the Bible 100%.  Ecumenicism can only really deal with what man says or adds to what is considered Christianity.  The Bible states what is necessary for spiritual unity and does not deal with the man created beliefs of denominations which differ from each other (which includes the Catholic church which I consider to be a denomination like the others).
God gave us the Bible to tell us what He wants us to know and do as well as The Holy Spirit to teach us to understand these things and guide us in our Christian walk.  Denominations that do not believe in a personal Holy Spirit that individually guides us and teaches us must use reason and tradition to guide them. This results in problems when man uses reasonings to interpret The Bible incorrectly in accordance with their belief in the way they believe a doctrine should be interpreted.  These become true bars to Ecumenicism but are dealt with Biblically and not through negotiation or discussion as their is really nothing to negotiate or discuss about.
Biblical error can never be negotiated or worked around so agreement and unity of fellowship can never occur while the error is maintained.
It is worse when th9ings not mentioned in The Bible are maintained as doctrine and are then the subject of ecumenical discussion to try and reach a common and mutual understanding.  By this Satan has wasted many hours of time when Christians could have been doing something more productive for THe Kingdom of God and even been fellowshipping.
Unity is only found in the true unity provided by Holy Spirit indwelling every follower of Jesus and will only occur as The Holy Spirit leads all concerned who are endeavouring to follow Jesus as their Lord.
There is nothing wrong with religious practices that other Christian faiths have providing:

Jesus is central to the activity
They are not against what the Bible teaches
They do not become idols
They do not break the Law of Love in any way

Jesus is King so every thing must be related back to He, His Kingdom and His Purposes otherwise it will be come idolatry in some way and this is perhaps the greatest danger in doing  things that are not in The Bible.  The Bible does have guidelines for doing things not mentioned in the Bible but the danger is that if you go outside these guidelines you will fall into idolatry.
In all things The Holy Spirit is your  guide and may ask you to do  things not in The Bible but then these will be for the purpose of the King and the Kingdom- and will not be idolatry.
The first matter to discuss is “what is a Christian?
A Christian is someone who wholeheartedly does their best to follow Jesus, in all they, do in the way they have been taught how too. Within their framework of their knowledge of whom Jesus is and His requirements of them they wholeheartedly try and follow Jesus.  This framework is learnt from their denomination and The Holy Spirit using The Bible and Godly men to teach them.
There may be error in their understanding of who Jesus as well as His requirements of them because they do not know the truths to counteract this error as they have not been taught them properly, if at all!  This does not stop them wholeheartedly doing all for Him, enduring hardship, trials and even death for His purposes (as they understand these to be) because they love Him so much.
The state of following Jesus while still having error in their doctrine is the position many Catholics are in as well as many Protestants. They only know what they are taught by ministers and then live their life according to this teaching. This is very true in poor Countries where people cannot read or write, or if they can, they cannot afford to purchase Bibles to study these things for themself.
The Church teachers and leaders will be judged for not meeting the needs of these people if they knowingly hide from them the truths that will free them from error.
These people, (both catholic and Protestant)  who have not been taught the truth, know only what is taught them and wholeheartedly serve Jesus as best they know in this framework of knowledge that they have been taught.  Their heart is perfect towards Him even though there is error in their understanding of their faith.  God looks at their heart and calls Him His adopted Children and accepts them as followers of His Son because of their heart attitude towards His Son.
These people cannot be blamed for not doing or understanding what they do not know because it is not taught to them. They cannot be blamed only for what they knowingly reject.
God expects you to work within the parameters you know and not within those you do not know. He also expects you to try and find out what you need to know as well as listen to The Holy Spirit as He tries to teach you these things, but this hearing The Holy Spirit is  possible only if you have been taught how to hear The Holy Spirit and also believe you can hear Him.
As long as a person is wholeheartedly willing to serve Jesus to the best of their knowledge and are willing to change when they are shown the truths they need to know, then no man can judge them.
It is when you are shown the truths you need to know and understand them but refuse to assimilate them into your Christian life that you condemn yourself through rejecting what the Holy Spirit has shown you and by this disobey God!  Knowingly continuing in this disobedience can cost you your salvation (Rev 3:5).
This book is a search for truth in the hope it will help set people free and assist them to draw closer to God!

Jn 8:31-32. Then said Jesus to those Jews which believed on him, If ye continue in my word, [then] are ye my disciples indeed;   And ye shall know the truth, and the truth shall make you free.
Jn 16:13  Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, [that] shall he speak: and he will shew you things to come.
Jn 7:16-17  Jesus answered them, and said, My doctrine is not mine, but his that sent me.  If any man will do his will, he shall know of the doctrine, whether it be of God, or [whether] I speak of myself.
Act 17:11  These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so.

The truth will be found if you are willing to accept it so that you are without excuse if you do not study The Bible or reject what it reveals to you directly or indirectly through others.
A Warning

Mat 5:30  And if thy right hand offend thee, cut it off, and cast it from thee: for it is profitable for thee that one of thy members should perish, and not that thy whole body should be cast into hell.
Mat 18:6  But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.

If you knowingly cause another to sin you risk going to hell.  If you know the truth and do not tell another who needs to know it or hide it from people, when The Holy Spirit has told you to tell them it, you risk going to hell through disobedience to Jesus.  He desires all to be free and the truth sets you free so if you do not tell others the truth that will set them free you are in disobedience and that if unrepented of can lose you your salvation (Rev 3:5)