You are misreading again and you brought Harmony in discussion that was not the question at first place. Jinnah said, we will live separately in peace. There was no harmony among Muslims as minority and Ruling Elite of British India. If there was harmony then there was no need of a separate Pakistan.
Yes, read Islamic Law for better understanding but Pakistan Constitution is not Islamic Shariah at all.
Not related but still to answer you, you interpret it for Secular State by Jinnah which is not correct. Muslim does not know any liberal secular etc thing but only Islam. Do you know what is secularism and then read Islam as well for better understanding. Minorities are well secure in Islam.
Your opinion and selective analysis from Indian prospect which could be contrary to the fact or not the right one so cannot generalize it.
For your overall post, Pakistan was never meant to be secular state. India can continue with its constitution but while mentioning the minority thing, I am again repeating shortly, read about caste system, the difference of practicing minorities rights in India and discrimination as well. Though not to cause derailing the topic here, these subjects are well discussed so there is no need of repetition at all. About living separately, indeed that is what Jinnah mentioned in earlier speeches so you can read and listen for better understanding that Pakistan was must due to discrimination by ruling elite in those times hence the need of separate country. To let you understand your secular Pakistan theory, there was no need of Pakistan if it was the idea and India was/is better in this. Indian constitution is equality and on the same time you see great inequality in India so how do you compare India's 70 years like mere equality in constitution which is not practiced, is benefiting the society at all. All in all, to conclude it shortly, Pakistan don't need any secular system and was never meant to be except the misleading and forged, cooked, concocted stories by libidos or secular. The name is Islamic Republic of Pakistan so there is no room for anything else.