No disrespect, but you put to much emphasis on God's law. It was not the law that unified them, it was the law that divided them. What united them was their common faith in the one true God.
Paul preached unity in Christ and Christ alone. Not a conformity to God's laws.
Hebrews 8:10-12
For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people: And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest. For I will be merciful to their unrighteousness, and their sins and their iniquities will I remember no more.
Catholics, Jehovah's Witness's, Mormons, Protestants.............. All have different beliefs about doctrine, but they ALL have a common faith in the one true God. We may each see him differently, but we all share that same common faith.
When shall we find unity? When we can lay down the scriptures and let go of the law so that we stop standing in judgement over one another's beliefs, religious or political, and accept the common faith that we have been called to walk in.
As for the forest and the trees, you seek for unity and condemn the division. But is it not the Lord himself who brings the division? Separating the sheep from the goats?
Luke 12:51-53
Suppose ye that I am come to give peace on earth? I tell you, Nay; but rather division: For from henceforth there shall be five in one house divided, three against two, and two against three. The father shall be divided against the son, and the son against the father; the mother against the daughter, and the daughter against the mother; the mother in law against her daughter in law, and the daughter in law against her mother in law.