Trust is not something that can be easily gained but very easily destroyed. Trust IS important, trust IS necessary, and trust IS foundational to any and all relationships - and in this post I am going to highlight some reasons why trust is important.
Here are two related posts that you may like to read: How to Gain Trust: 4 Tips and 6 Means to Regain Trust.
Having a level of trust will mean that you are dependable and that is something that is essential in a relationship. If someone is trustworthy then you know that you can depend on them whatever the circumstance.
The other person in the relationship will want to be able to rely on you also and having the assurance that they can do so, it is something that works both ways.
Without trust how can you be open with one another? Openness is where you can share information with each other, personal and private information, and have the confidence that they will be not only understanding but also trustworthy enough not to run around telling everyone. Think what it would be like in a relationship if you couldn't be open with one another because the trust didn't exist - who could you turn to in times of hardship, how could you express some of you deepest emotions with that person if you couldn't trust them, and how could they do the same with you if they couldn't trust you?
3. Less Stress
If you can't trust somebody then it is likely that anxiety will become a factor in your daily life. A relationship without trust will cause stress and will likely cause friction between the two of you. How can you relax when trust is not one of the foundations which your relationship is built upon?, thus stress and anxiety will arise, possibly forcing your relationship apart.
Having trust will mean that there won't be the need to worry about the other person, anxiety and stress if you have any wont be the result of trust issues.