mad-bhakta-pujabhyadhika (Shrimad Bhagavatam 11.19.21):
The worship of my devotees is higher than even My own worship.
Sri Ramanujacarya has stated:
The worship of Vaisnavas is greater than the worship of the Supreme Lord. Insulting a Vaisnava is more offensive than insulting Lord Visnu. The water that has washed the feet of a devotee is more pure than the water that has washed the feet of Gauranga-Krsna. There is no higher achievement than to worship a Vaisnava. There is nothing more offensive than being envious of a Vaisnava, which results in one's utter ruination. One should always converse with maha-bhagavata Vaisnavas, and one should never see the lowest of mankind who criticizesVaisnavas. One should never reside with a duplicitous person who is attached to sense gratification and decorated with the signs of a Vaisnava
Adi Purana:ye me bhakta-janah partha
na me bhaktas ca te janah
mad-bhaktanam ca ye bhaktas
te me bhakta-tama matah
`Those who are My direct devotees are actually not My devotees, but those who are the devotees and worshipers of My devotees are factually My devotees.'
Shri Chaitanya Charitamrita Madhya Lila 11.31:
visnor aradhanam param
tasmat parataram devi
`Lord Siva to Parvati: My dear Devi, although the Vedas recommend worship of demigods, the worship of Lord Visnu is topmost. However, above the worship of Lord Visnu is the rendering of worshipful service to the Vaisnavas, who are devoted to Lord Visnu.'
Srila Prabhupada Letter to Sudama
Yes, Krishna is never approached directly. Krishna is approached through His bona fide servitors. He says that, "Carrying out the order of My pure devotee is greater than carrying out that directly given by Me." In this connection, I may inform you that you try your best to serve Krishna under the direction of your Spiritual Master and Krishna will surely help you in all respects.