If we ought to be willing to lay down our lives for others, we ought to be willing to make those comparatively smaller sacrifices which are necessary to relieve them in their distresses. Unless we are willing to do this, we can have no evidence that the love of God dwells in us. We can show love through our words, but John seems to be saying this is an inferior form of love. He doesn't say to love in word AND deed - he suggests we don't even express our love through words IF it means we are going to fail to love in deed, through our actions.
We can't accomplish this without being saved - true salvation bears fruits of love. In the world, love does exist - but without God it has its limits. It is the Spirit of Christ within us that allows us to die to self and then learn to love as He loved. So while love and loving actions are very much part of essential Christian living, Jesus made it clear that without Him leading the way the love and wonderful works are empty. The Spirit is constantly calling to all who believe on Jesus Christ to live as He lived, to love as He loved, to be Him to all we see and hear. When this occurs, we can be confident in our hearts that God is with us, and we are with Him.
While it's true we have false prophets run amok today, who are more false teachers than those claiming to actually be prophets, John's advice in these verses was to them who were surrounded with divisions and threats to the faith. What John was really warning them about was people who claimed to be speaking for God. The claim at hand was that Christ was not a man of flesh and blood. John was there to tell them otherwise. He says here that every spirit that admits Jesus Christ came in the flesh is of God. He doesn't say this confession makes them a Christian or a saved individual. This is a starting point for us as believers when talking with people - do they believe that Jesus came in the flesh?