Why does religion matter? Why not love God and leave religion aside?
Assallam alaikum. Thank you for asking about Islam. It is our pleasure and our duty to have the opportunity to clarify questions about Islam.
Let us suppose there is a person named Rose. And she loves everything. Dogs, cats, sheep, trees, her parents - mother and father, sister, brother, humanity... God. Does it make sense to put all of them under the column of love? Perhaps for some people, but Rose puts Love of God at a much higher plane; she worships God - the highest form of love.
Rose loves her cat, she loves her best friend, she loves her partner, she loves her parents. She likes her car, and she loves to go skiing. Rose is a very determined woman and she loves her career. She is a doctor, and she loves her job of saving people. But she worships only One God. Because God created her, and gave her everything she has - everything! And there is no one else who loves her more than Him.
Neither is there anyone comparable to Him; He has no children, no parents, is Eternal, and Absolute. Nothing can compare to Him in His Majesty. Consider the vastness of creation, its truly beyond our capacity to even comprehend! And how much greater must be the Creator?
And that Creator, wants Rose to worship Him, not just love Him but the highest form of love. Rose knows this, but she wants to be sure that she worships Him the way He wishes to be worshiped. After all, if she loves her cat - Tommy, she will make sure she gets her the kind of food the cat wants, and not for instance dog food (which presumably Tommy doesn't like). If she loves her job, she will try to wear the kind of clothes that are appropriate for her hospital, not the kind of clothes she wears to the nightclub. If she loves her dad and she knows that her dad hates purple, she won't get him a purple tie as a gift.
So, if Rose truly worshiped God, she would worship Him the way He wishes to be worshiped, and not for instance in ways that He doesn't like or even specifically detests. So how can she know how God wishes her to worship Him? Rose thought about this and pondered over the question.
At length Rose prayed to God to guide her, and started a diligent research, searching for the truth. She looked into the Bible, the Torah, the Quran, Vedas... She finds that each of them says something different, often spectacularly different, even completely opposite things. So she needs a litmus test, a way to logically and reasonably find out which of these are the truth, and which others have been corrupted, perhaps by the hands of men; i.e. how does God really want her to worship Him?
Rose finds that only the Quran has irrefutably remained the same without being corrupted, and she finds that there is even a huge amount of scientific evidence that anyone who objectively makes a study searching for how to worship God, cannot ignore.
Now, imagine that Rose now knows this - that the Quran is the Truth, and unlike other Scriptures, has not been corrupted. She feels conflicted. She was born a Christian, and her parents raised her as a Christian. Will she remain Christian?
Rose decides not to, because she loves to the highest degree - worships Allah, not her parents, not her culture, not her heritage. Now she knows how her Creator wishes her to worship Him. And she will not let anything else get in the way of that.
I hope that explains why following the right religion matters. In truth, Islam is not really a religion but the natural way of being for all humanity. It is also a complete way of life and not just something people do on a specific day or time alone.