Purport

This Shloka gives the answer to one of the biggest questions of modern time or perhaps from ancient times too. Which worship is better? 1. Worshipping a manifest God 2. Worshipping an invisible God?
Arjuna asked the question above Shloka#1. Bhagvan Shri Krishna very clearly answered in Shloka#2 that worshipping a manifest God is best.

In this Shloka Bhagvan Shri Krishna answers why worshipping a manifest God, i.e God with a form or Form of God is best?

There are two reasons 1. Worshipping an invisible God is extremely difficult.2. Progress in such discipline of worship is very hard to make and so chances to succeed in that path is less. 

Bhagvan Shri Krishna also pointed out why it is difficult for human beings to worship invisible God and make progress? A human being himself is an embodied being. The human mind and senses are designed to understand only material things and material changes. However some absolute concepts can be understood through inferences and secondary observations, but again the secondary observations must be a material thing. For example, when humans cant grasps the field of gravitation through their senses and mind, but they can observe the phenomena of gravitation when they see an object when dropped from height comes down to earth. Understanding any absolute definition or phenomenon is beyond the human mind. For example when we say God is infinite, what exactly can we understand? Does infinite mean anything? The moment we read this word infinitely and try to understand our mind starts wandering into different visible things. Many of them just look at the sky and try to assume God is something like the sky. Many others may think of the ocean and try to assume God is like an ocean. 

Similarly, when one says God is omnipotent, what exactly he understands? Some people may start thinking of a very powerful wrestler around their area and try to assume God is like him. Some others may think of superman, flying in the sky, carrying mountains, so on and so forth. Another example, what does one mean when he says God is omnipresent? If a person tries to understand this he will start thinking of everything around him, T stone, mud, leaves, pond, river? This is only going to confuse that person. In fact, he may go into deeper trouble when he would be asked is God in gutter also?

The summary is that no absolute definition or concept can be grasped by must of human. There might be few people who are of the level of Einstein may still able to comprehend some absolute concept. But we know not everybody is like Einstein. So understanding absolute is not impossible but extremely difficult. Thus those who follow a God as an absolute entity having some absolute attributes are mostly get lost into the random things. Most of them fail to achieve the purpose of worship and hence their efforts may fail.

On the other hand, worshipping a God with form is very easy. One devotee who worships Shri Krishna, Shri Ram finds it so easy to fix his mind. He does not have to even know a lot of scriptures. He simply knows some acts of Shri Krishna and Shri Ram and portrays their acts in the form of statues, pictures, etc and they achieve a perfect state of devotion. Worshipping of God with form is what called Idol worship and hence from this verse, it becomes very clear that Idol worship is the best form of worship. It’s easy to follow and has a high rate of success.

However, there are many prescribed methods to follow the path of worshipping invisible God without using any rituals or physical methods, like Meditation, Tapasya, and practice of Ashtanga yoga. But none of this path is easy and requires strong dedication and time. And to further specify, the methods of meditation, Tapasya and Ashtanga yoga is available only in Hinduism and Buddhism up to a limit. it's also available in Sikhism and Jainism. But beyond that other who try to worship an invisible God through somebody's gestures and uttering, words are probably doing so in vain. They will not achieve any state of enlightenment nor will they realize any benefits of worship in a human lifetime