If all living beings can be seen due to having a form, then why can’t the creator of all living beings also be seen due to having a form?
If all living beings have a birthday, then why can’t the creator also have a birthday for when He appears on this planet?
Shri Krishna Janmashtami is the birthday of Lord Krishna. God is unborn, but still He appears in His original spiritual form to exhibit His transcendental forms and activities.
We come out from the womb of a woman and are naked. Lord Krishna did not come out from the womb of a woman. He appeared next to a woman, fully clothed and as an adult. Then He transformed Himself into a baby so that He can enjoy the loving personal relationship with His devotees. Just like any loving father would want to see, live, and play with his children.
Lord Krishna appeared about 5,000 years ago and performed His transcendental pastimes for 125 years before going back to His abode. He had a spiritual body.
“Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion – at that time I descend Myself. To deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I Myself appear, millennium after millennium.” (Lord Krishna, Bhagavad-Gita 4.7-8)
The millennium in the above verse means every 8.64 billion years and not 1,000 years. Lord Krishna appears in His original form, once every 8.64 billion years in this universe. He also appears in millions of other universes to perform His transcendental pastimes.
The above is a secondary reason why Lord Krishna appears. The primary reason is to fulfill the wishes of His devotees to see Him and He also wants to enjoy the association with His devotees.