Well, not to be overly obvious, but your friend’s assertion of “All one must do to be saved is love Jesus” itself negates his proposed philosophical position.
First, he is weilding it both in a dogmatic fasion, and as a definitive truth which he says cannot exist. He has denied his own faith.
Second, Christ is very clear in the bible that not all who call upon him will be saved by him. While he clearly intends that the target of this assertion is anyone but him, he has (and can not have according to his stated position) no means of being assured of such.
Third, if dogma/teaching was of so little importance, then why did Jesus bother? Or further, why did he bother correcting the false conclusions of anyone if all they needed was to love him? Why did Jesus specifically condemn doctrine in the Apocalyse if it didn’t matter? Clearly, Jesus felt that doctrine/dogma was important.
Fourth, and related to #3, If God, presumably the only absolute truth, expressed said truth, but there cannot be said truth according to his relativism, did God Lie? Or is your friend an Arian, and denies the divinity of Christ? Or is Christ just the invention of the Apostles?
A very important point of the Incarnation is an unavoidable refutation of relativism. Either God was incarnated as Jesus, or he was not; such is an absolute position not made real either by faith or lack thereof. It either happened or it did not, wholly independant of our acceptance of its fact. That one cannot be materially certain to it does not validate some false application of the Uncertainty Principle that makes the issue now flexible. Does your freind really believe that the Incarnation of Christ is made real only because he happens to believe in it?
What about when Christ said, there is only one way? He never said “All you have to do is love me”, but did say a great deal of things that suggest there is an exacting Way that leads to God, none of which included a nebulous emotional response.
Yes, relativism, especially in the moral field, is a wonderful thing for those wanting to do their own thing and on their own terms. But that is not what Christ gave us, unless you reject that he gave us anything, including himself. Complexity does not create anything more than the illusion of flexibility, the principles always remain absolute.
He should also read the Colossians passage in its fullness for context. This passage does not condemn the Church, but those who will condemn it because of these things. As the Church uses them in a manner which recognizes them as “mere shadows” which lead to the substance of Chirst, there is no conflict for us. There is one for those who eleveate the shadow to the status of Substance, which becomes idolatry, and then ( in the case of your friend), reject them in their disfigured form. It is a strange irony that those who accuse the Church of such idolotry are themselves the idolators.
If it is his intent that because we are not to judge and therefore there is no standard, then he needs a friendly reminder that God has insisted that He is going to judge; therefore, there is a determined standard by which all things will be set. It just simply means that we don’t get to set that standard, as many philosophical quantum theorists/moral relativists want to insist.
The list can go on, but I gots work (and sleep) to accomplish
