You may wonder why lingerie is so important when it comes to your bridal trousseau. The key reason is that even though the actual lingerie cannot be seen by everyone, the effect and fit of the lingerie can. So if you are wearing a very expensive kurta or salwar kameez but your bra doesn't fit, the entire effect of your outfit will be ruined. If you have a large bust and your bra isn't giving you full support, then your bust will tend to sag -- it will make your body look bigger, as your bust sits over the top of your stomach.
Lingerie is often referred to as foundationwear because it is the foundation of your look and as we all know, unless the foundations work, nothing else will.
It is also important to remember that one bra does not work for all purposes. In the same way that one handbag or pair of shoes cannot be worn with every outfit, your outfits all have different looks, shapes and fabric; it is important that you have a wardrobe of lingerie to complement them.
Also see: Questions to ask before saying 'I do'