Love. What is written by the finger of God on men’s hearts.
The unity we have is unity in the Spirit.
I don't recall anywhere where Scripture relates to us a *law of love*.
Ephesians 4 1-3 1 I therefore, a prisoner for the Lord, urge you to walk in a manner worthy of the calling to which you have been called, 2 with all humility and gentleness, with patience, bearing with one another in love, 3 eager to maintain the unity of the Spirit in the bond of peace.
We are united to Christ and so in an indirect sense to each other through that, but that in no way indicates that we can or are permitted to contact those who are no longer living on this earth in our physical bodies. The prohibitions against contacting the dead have always been understood to mean those who have died physically, Catholic semantics notwithstanding.
Just because they are alive spiritually somewhere, which everyone is whether they're saved or not, is not enough to justify contacting them when God so clearly prohibits it.