1John 3:18-20 Dear children, let us not love with words or tongue but with actions and in truth. This then is how we know that we belong to the truth, and how we set our hearts at rest in his presence whenever our hearts condemn us. For God is greater than our hearts, and he knows everything.
How do you know whether you belong to the truth? By evaluating whether your love is simply lip service or whether you actually love in actions and in the truth. Consider Jesus. He loved in action by healing diseases and by dying on the cross, among other things. He loved in truth by his teachings. Christians are to love by meeting people's real needs in action and by teaching them the truth. If you're just involved in meeting practical needs, that is not Jesus' example.
Few object to having their practical needs met, but they may have a hostile reaction when you tell them the truth. In view of this fact many Christians may opt to do the one without the other, or even introduce false ideas. "The only reason they do this is to avoid being persecuted for the cross of Christ." Gal 6:12From time to time our heart will condemn us - whether for legitimate or illegitimate reasons. But if we evaluate our lives as Paul writes, "Examine yourselves to see whether you are in the faith; test yourselves. Do you not realize that Christ Jesus is in you— unless, of course, you fail the test?" 2Cor 13:5, and if we determine our love is genuine, John is saying that this fact is meant to give us a feeling of assurance of salvation.
Assurance of Salvation is not simply based upon our claims of faith. It is based upon those measurable and inevitable effects of being born of God, such as genuine love for fellow Christians.