Before starting Japa or Puja, one should touch his Shikha chanting a mantra “शक्त्यै शिखायै वैषट्”. So if Shikha is not there, one is not even eligible for Japa or Puja. Sushrut says “तत्रापि सद्यो मरणं मस्तकाभ्यन्तरोपरिष्ठात् सिरासन्धिसन्निपातो रोमावर्तोऽधिपतिः तत्रापि सद्य एव” The supreme sensitive spot on the head is Adhipati Marma, where is the nexus of all nerves, and a joint. An injury to the Adhipati Marma the verticalgroove on the frontal bone, which is marhed in the inner side of the roof of cranium by the Sira Sannipata (superior langtitutinal sinus) and on the exterior side by the ringlet of the hair (Romavarta) proves fatal within the day. (Sushrut Samhitã 6/71). Below this pint lies Brahmarandhra where Sushama Nadi arrives from the lower part of the body. Yoga Shastra describes Brahmarandhra is the highest point known as Seventh Chakrs. Shikha protects this point, hence Shikha is significant.
Yajnopavitam (यज्ञोपवीतम्) is a symbolic triad thread worn by Brahmana, Kshatriya and Vaishya. This thread is symbol to that one is eligible for performing Yajnas. यज्ञोपवीतम् means यज्ञार्थम् उपवीतम् i.e. thread worn for sacrifice. This thread makes one eligible to perform Yagaas. It is said – यज्ञोपवीतं परमं पवित्रं प्रजापतेः यत्सहजं पुरस्तात् । आयुष्यम् अग्र्यं प्रतिमुञ्च शुभ्रं यज्ञोपवीतं बलमस्तु तेजः ॥ Meaning wearing this most sacred thread gives us long-life, strength etc. Some acts have direct benefits and some have indirect benefits. This has direct and indirect benefits. Direct is making us eligible for performing Yagaas and Pujas and gives us long life etc. Indirect is it is said as “sacred” which though does not have any direct benefit; it will help us to go near the ultimate wisdom (a belief). This thread is of various types and made of various materials.