Pure devotional service is for intelligent people; the others, who take to worshipping the demigods, are not so intelligent. The Vedas describe different types of worship for different classes of people. The real purpose of the Vedas is not that one be satisfied with some material gain by demi god worship or sacrifice. The less intelligent persons are advised to worship specific demi gods and gradually they are brought to the level of understanding that they have to be sanctioned by the master of all demi gods, Lord Vishnu. A reminder is always given, when there is death or when one realizes that material benefits are temporary. Krishna summarizes the entire Vedic knowledge and gives the real essence. The bulk of the Vedas is called the karma kanda portion because most of the people in this world are interested only in material enjoyment so that at least through performing sacrifices or worshiping demi gods; even without their knowledge they are coming in contact with the Supreme Lord. Nonetheless by even indirect contact with the Supreme Lord, a person is elevated to a higher status, his intelligence becomes broadened. This is the real spiritual advancement of knowledge.
A human being has developed intelligence to recognize that relative truth is not truth because he sees that it is not true in all phases of time. Therefore he gives up this relative truth and wants to progress to the realm of Absolute Truth. One comes to the platform of knowledge beyond simply desiring some material gain. Prabhupada says dharmartha uttama slokam - one should worship Lord Vishnu or His devotee for spiritual advancement in knowledge.
Krishna says that body is temporary but you are not the body, you are spirit soul. Systematically Krishna is taking us through all these different realizations on the path of spiritual advancement and summarizing the whole range of Vedic instruction. Especially in Kali yuga it is not possible that people may actually take the advantage of the human form of life by gradual elevation through following the Vedic directions. That’s why the Bhagavad gita and Bhagavatam are meant for people in Kali yuga.
Bhagavad gita is described as the preliminary study of Bhagavatam. Simply by hearing the Bhagavatam, one is able to satisfy all his desires even for material enjoyment, it also results in purification of the heart. Spiritual advancement of knowledge means there has to be a change of heart, becoming more intelligent in that one’s enquiry is not simply how I can elevate myself through different levels of material advancement but how I can come to the point of enquiring about the Absolute Truth. This is made possible by taking to worship of Krishna or through pure devotional service. Direct contact with Krishna means one is able to make very quick progress on the path of spiritual advancement; which means one becomes wise by surrendering to Krishna and become His devotee. One gives up all pursuit of material desires including the desire for liberation - moksa kama, sarva kamo. This is really broadening one’s intelligence udara dhih, the benefit of pure devotional service.
Therefore Sukadev Goswami even though in the beginning he says one may worship the virat rupa of the Lord or one may worship the form of the Lord in the heart - paramatma but ultimately he concludes by telling - best is you worship directly the Supreme Personality of Godhead in His feature as Bhagavan.