Yes, if it is Gur mantra chanting the name of Akal Purakh all the time, then I agree with you. But if we follow the dera walas mantar or gayatri mantar (glorifying deities) or as stated above wealth, girls, then it will not help us to cross bhavjal.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/spiritual-articles/5364-mantra-and-thought.html
Regards Sahni Mohinder