How do you know the church is true? That's a matter of your own interpretation as well. You've decided that the church is right based on what?
It's the same dilemma whether you are trying to determine the truth using Scripture, or using the church.
The very weaknesses Catholics like to try to point out when people rely on Scripture, are the very same weaknesses that exist when people try to rely on the church.
Who interprets the church to you?
Who interprets the catechism to you?
Who interprets the magisterium to you?
Who interprets the priests homily to you?
Who interprets the interpretation of the interpreter to you.
And so it goes.
What's true is NOT the church. Nowhere in Scripture is the church ever called the truth or are we told to look to the church for the truth.
On the contrary, this is what the Holy Spirit in Scripture is the truth.
John 14:6 Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me.
John 17:17 Sanctify them in the truth; your word is truth.
So tell me, what's so hard about that to understand that I need someone to *interpret* it for me? That I can't understand that on my own?
All protestants are their own authority, just ask one, they all know the Bible better the next one. In the protestant mind, “Me and Jesus we got a good thing going, we don’t need no stinkin’ church to tell us what it’s all about”. We don’t need to get baptised and we don’t need to go to no stinkin’ church”.
You ask some really good questions.
How do you know the Church is true? A person has to decide whether what each church proposes for belief is most reasonable to them. Some use the four marks of the true church, others don’t. That’s why our relationship with God is personal. We have to use our intellect and discernment.
Unfortunately, you create a false choice saying people either rely on the Church or the Scripture. Instead, Catholics use both. It is the Scripture and the writings of the Apostles and Disciples BEFORE the Bible was assembled, which form the basis of Catholic belief and teaching.
In the next set of questions, a person must discern whether they believe what is being proposed for belief. The Catechism if pretty clear (in an academic way), and also points out places where the Church takes no position.
A person can rely on his Bishop for proper teaching and interpretation. The Bishops, in union with the Pope, deal with difficult issues. Ultimately, the Pope decides, based on a number of factors, which is the right course. The individual must then decide if they should stay or go. An interesting note, Paul VI, after having several commissions of experts, etc study artificial contraception, wrote Humanae Vitae. This was an outright rejection of the prevailing attitude of the time, and a reassertion of the traditional Catholic teaching.
You create a straw man by suggesting the Truth is the Church. No, Jesus is the Truth. The Church is the physical structure on Earth that teaches what Jesus taught, following the grand commission.
People have a natural right to decide what and how they will believe. An intellect, well-formed conscience, and discernment, and ultimately the Holy Spirit point people to God. Are all religions equivalent? No. Fortunately, God is ever-merciful and decides who will and who will not enter Heaven.