Why is it necessary to chant the name of God?

Īśo'haṃ sarvajagatāṃ nāmnāṃ viṣṇorhi jāpakaḥ।
Satyaṃ satyaṃ vadāmyeva harernānyā gatirnṛṇām॥

Lord Shankar says to Mother Parvati:-

Even though I am the Lord of the whole world, I chant the name of Lord Vishnu. I am telling you the truth, there is no other way for living beings except God.

Kaler doṣa-nidhe rājan, asti hy eko mahān guṇaḥ।
Kīrtanād eva kṛṣṇasya, mukta-saṅgaḥ paraṃ vrajet॥

- Shrimad Bhagwat Mahapuran (12.3.51)

Parikshit! Although Kaliyug is a treasure trove of faults, it has one great virtue. That virtue is that in Kaliyug, just by chanting the name of Lord Shri Krishna, all attachments are released and one attains God.

Kṛte yad dhyāyato viṣṇuṃ, tretāyāṃ yajato makhaiḥ।
Dvāpare paricaryāyāṃ, kalau tad dhari-kīrtanāt॥

- Shrimad Bhagwat Mahapuran (12.3.52)

The fruits that are obtained by meditating on God in Satya Yuga, by worshipping Him through big yagyas in Treta Yuga, and by worshipping Him according to the prescribed rituals in Dwapar Yuga can be obtained in Kali Yuga(present) by simply chanting the Lord's name(Madhav).