Gurbani has two-fold mission. It is Guru-roop and it is Mantra-roop. Being our Guru, it shows us the way to Vaheguru. In order to fully understand Gurmat, it is imperative that Gurbani be understood but as per Gurbani, there are very rare ones who do vichaar on Gurbani:
ਬਾਣੀ ਬਿਰਲਉ ਬੀਚਾਰਸੀ ਜੇ ਕੋ ਗੁਰਮੁਖਿ ਹੋਇ ॥ ਇਹ ਬਾਣੀ ਮਹਾ ਪੁਰਖ ਕੀ ਨਿਜ ਘਰਿ ਵਾਸਾ ਹੋਇ ॥੪੦॥
(Only a rare person contemplates on Gurbani and such person can do so only if he is a Gurmukh. This Baani of great Purakh is such that who ever contemplates on it, finds residence in real personal abode.)
The above reference from Gurbani leaves no doubt that an effort should be made to understand Gurbani. Another important thing is that this understanding should come directly from Gurbani and not from translations. In the beginning and even at later stages one has to refer to translations done by Gurmukhs but as one progresses spiritually, one finds that Gurbani itself reveals itself to the one who serves it (does paath with shardha). Effort should be made to understand words used in Gurbani and also an attempt should be made to understand the basic grammar of Gurbani. It greatly assists one in understanding Gurbani.
If one understands Gurbani, it greatly enhances the Vismaad one gets from listening to Kirtan or Paath. Without understanding, this Vismaad is hard to get.
The second function of Gurbani is that it is Mantra-roop. Mantra is such word or combination of words that if spoken with a certain maryada, yield results. It does not matter if one understands the meaning of Mantra or not; it still has effect. It does not matter whether one knows the nature of fire or not. If one brings one's hand near fire it will burn. Same way, whether one knows that water cleans one's body or not, it still cleans it. Similarly, Gurbani cleans one's inside. When one does paath of Gurbani and listens attentively to the sound of Gurbani, it has an enchanting and life-changing effect on the seeker. Just by listening to Gurbani one's sorrows and pains are removed. One becomes close to Vaheguru. Amritdhari Gursikhs know that when one does paath of Gurbani with maryada, automatically and effortlessly, the Naam Abhyaas from within starts. One's mind wants to japp Naam. This is the Paaras Kala of Gurbani.
Does water understand the meaning of Gurbani? No. But still it turns into Amrit when Gurbani Paath is done in its vicinity. What else is the Khande di Pahul? If we take away Gurbani from it, what is left behind? Just sweet water. So it is proven beyond doubt that it is the paath of 5 Amrit Baanis that turn the sweet water into Amrit. Water does not understand Gurbani but it still turns into Amrit. Our body too is 75% water. Would it not turn into Amrit, if Gurbani paath is done with maryada. In other words, the whole body would turn into Amrit, if paath would be done with Maryada. Can any disease remain in the body then?
The four pauris of Suniai in Siri Jap jee Sahib teach us the greatness of listening to Naam and Gurbani. Just by hearing it, one's sorrows are removed but the condition is that one MUST HEAR GURBANI. If we do paath and our concentration is not in Gurbani, then too the benefit is there but at a very low level. The full effect comes with listening to Gurbani, while doing paath of it.
May Guru Sahib enable us to do vichaar of Gurbani and listen to Gurbani with full maryada.