Religion: a set of beliefs concerning the cause, nature, and purpose of the universe, especially when considered as the creation of a super human agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
Now, that is a mouthful! Yet, if I read it again and again, it really says nothing to me to define what Paul might have been thinking about when he reminded Timothy of the importance of "religion" as guiding one's life, keeping one on track, and giving purpose to all of life's actions. There is a closer definition which is also listed in the dictionary which really indicates "religion" as something which "alters" our way of living. I think this is probably what Paul had in mind - a set of values and beliefs which alter our way of living - affecting choices repeatedly until they come into alignment with one believes.
As the saying goes, “Exercise is good for your body, but religion helps you in every way. It promises life now and forever.” These words are worthwhile and should not be forgotten. (I Timothy 4:8-9 CEV)
Just as exercise is good for the body, the set of values (morals) and beliefs (standards) we choose to hold onto in life determine how we will respond to life's challenges. For example, if one of the values we adhere to is honesty, then when it comes time to do our taxes, we will likely read through the instruction booklet and adhere closely to what it says we are allowed to claim as deductions. If we accidentally claim something without knowledge of the error, we won't feel any conviction in doing so until the claim is rejected or our inaccuracy is discovered. The morals which guide us (honesty) will cause us to amend our return - accepting a lesser return or even paying a tax based on the error. Why? We have a set of values which guide our actions - any deviation from that set of values will cause us something we refer to as guilt.
Physical exercise helps the body stay in shape - giving our body form and endurance which will help us in many ways. Yet, a "toned" body does very little to help us be honest on our taxes! It doesn't keep us respectful of one another's feelings. It cannot give us the integrity to remain faithful to vows we have made to God or one another. It is simply a way of ensuring our physical body is in the best shape it can be in to respond to life everyday. The challenges of the mind, heart, and will are something we need this thing called "religion" to help us sort out. These set of beliefs are what give us the minimum set of "standards" by which we respond to these tests of the will, unease of the heart, and stubbornness of the will.
If this holds true, then we need to ensure the set of values we adhere to are very closely aligned with what scripture reveals. Any deviation from the scriptural truths will produce a flawed set of values and has the capacity of influencing our choices in a negative manner. This is why it is dangerous to have a "religion" which is based on personal opinion or a man's (woman's) "personal revelation" of "truth". Man's "personal revelation" or "opinion" is dangerously flawed by how it is we see each other, ourselves, and even our appreciation of the holiness of God. For example, if we see our "revelation" as superior to the holy scriptures, we will be "adding to" scripture teachings which are based on some "personal experience" we have had. As scripture plainly points out, it is unacceptable to add to or take away from scripture - the man/woman who does so is going to be judged very severely. "Everything God says is true—and it’s a shield for all who come to him for safety. Don’t change what God has said! He will correct you and show that you are a liar." (Proverbs 30:5-6 CEV)
Be cautious about the set of values you adhere to - for they matter more than you know. It is more than a "denomination" which makes the difference. It is the entirety of what we believe which settles the truth within our hearts and minds, guiding our actions. Just sayin!