Can you explain the significance of Waheguru in the Sikh concept of Bhakti and the importance of devotion in the faith?

ਸਤਿਕਾਰ ਯੋਗ ਨਿੱਕੀ ਕੌਰ ਜੀ,
ਵਾਹਿਗੁਰੂ ਜੀ ਕਾ ਖ਼ਾਲਸਾ ਵਾਹਿਗੁਰੂ ਜੀ ਕੀ ਫ਼ਤਹਿ।।

In response to your question, as understood by the undersigned, the word Waheguru is combination of two words ‘Wahe (ਵਾਹਿ), which means Akalpurakh/Parmatma, who deserves praise/admiration/laudation/compliment and ‘Guru (ਗੁਰੂ)’, which means Akalpurakh/Parmatma, who is kind to impart knowledge, in darkness of ignorance.

Here the undersigned will like to add that in Sikhism, Akalpurakh and Guru are embodiment of each other.

In Raag Asa, at Panna 358 of Guru Granth Sahib, Fourth Guru Person Guru Ramdas Sahib is guiding, in the stanza of Rahao, that Akalpurakh/Parmatma has many names, appearances, limitless virtues, which can’t be described by anyone.

Now coming to the Sikh concept of Bhakti and importance of devotion in the faith, as understood by the undersigned, there is no place for reçiting any word, as mantra, but necessity is of imbibing the teachings of Guru Granth Sahib, changing one’s life, getting rid of vices and achieving emancipation/salvation during this life time, as Sikhism doesn’t subscribe to the concept of emancipation/salvation after death.

Hope this helps. If you have any further questions, please do ask. If you find any deficiencies, please point out the same, for improvement in future.

Regards,
Your Brother
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ਤਉ ਕਾਰਣਿ ਸਾਹਿਬਾ ਰੰਗਿ ਰਤੇ ॥ ਤੇਰੇ ਨਾਮ ਅਨੇਕਾ ਰੂਪ ਅਨੰਤਾ ਕਹਣੁ ਨ ਜਾਹੀ ਤੇਰੇ ਗੁਣ ਕੇਤੇ ॥੧॥ ਰਹਾਉ ॥ (ਪੰਨਾ 358)
ਅਰਥ: ਹੇ ਮੇਰੇ ਮਾਲਿਕ! ਤੈਨੂੰ ਮਿਲਣ ਲਈ ਅਨੇਕਾਂ ਬੰਦੇ ਤੇਰੇ ਪਿਆਰ ਵਿਚ ਰੰਗੇ ਰਹਿੰਦੇ ਹਨ। ਤੇਰੇ ਅਨੇਕਾਂ ਨਾਮ ਹਨ, ਤੇਰੇ ਬੇਅੰਤ ਰੂਪ ਹਨ, ਤੇਰੇ ਬੇਅੰਤ ਹੀ ਗੁਣ ਹਨ, ਕਿਸੇ ਭੀ ਪਾਸੋਂ ਬਿਆਨ ਨਹੀਂ ਕੀਤੇ ਜਾ ਸਕਦੇ।1। ਰਹਾਉ।