1Jn 2:1 My dear children, I write this to you so that you will not sin. But if anybody does sin, we have one who speaks to the Father in our defense— Jesus Christ, the Righteous One
Jesus is our defense attorney such that we need not be concerned of speaking in our own defense on the judgement day as others must. Jesus speaks on our behalf. So in answer to the question as to how you should respond if God were to ask you on the judgement day, "Why should I let you into my kingdom?", you only need answer, "You'll have to talk to my attorney. He's sitting at your right hand side."
Another thing from this verse is the fact that though our sins are forgiven, this does not imply we have a license to sin. Much to the contrary, for Jesus "gave himself for us to redeem us from all wickedness and to purify for himself a people that are his very own, eager to do what is good." Titus 2;14 But at the same time, realize that those born of God might sin from time to time. The verse "does sin" is in the Aorist tense. It is not referring to one's lifestyle, but to events which occur from time to time uncharacteristic of one's lifestyle.