The work of Jesus occurred on two levels, if you will.
The first is the reconciliation of the world to God. The entire race and creation now has access to God. This is the reversal of Adam's blunder and what Paul attributes to Jesus as the Second Adam.
All things are set right; God and the creation are no longer at enmity with each other. If Adam was the spokesman for humankind, Jesus is now. This is reminiscent of Boaz redeeming Ruth. Ruth didn't have to do anything before Boaz could redeem her. This redemption is actually a family responsibility thus, Boaz looking for whoever had the right of redeemer.
This redemption is grace on Boaz's part; he loves Ruth and he wants to set her life right.
This is the first level of Jesus's work. The second level is you, specifically. If the world has been reconciled, so have you in some sense. That sense is that you, as a human are reconciled to God through the redemption effected by Jesus.
Your job is the same as Ruth's was - to accept the redemption and reconciliation, and join God. When you do this, you "enter" the redemption and reconciliation. Paul will call this "in Christ" because it is in Christ that the redemption and reconciliation are.
What about your sins; don't they have to go away? Well yes, and no. If you enter Christ, if you accept the redemption and reconciliation as did Ruth, whatever you've done before this is simply not considered. Sins are not so much forgiven as they are not even noticed. This is sometimes called removing your sins as far as the east is from the west. They don't actually go anywhere and God doesn't "pretend" they no longer exist. In reality, God simply doesn't take note of them. Ruth's obligation is now to remain faithful and as long as she does, she is loved and cared for.
In this connection, read Isaiah 44.22, "I have blotted out your transgressions like a cloud and your sins like mist; return to me, for I have redeemed you" (ESV). Did you notice that flow? God had already blotted out the sin of his people, and then pleads with them to return to him. There is no longer an obstacle to their return, no hate from God, no penance or punishment to accomplish, nothing, wanting only their own desire for God. Similarly, and in a real sense, your sins were forgiven when Jesus reconciled the world to God. If you want to take advantage of that, simply accept God's invitation to life. That's what he wants and that's why he doesn't worry about your sins - he wanted you enough to reconcile himself to you even before you even knew you had sin.
So what happens to Ruth if she blows it after she's been redeemed? Does that change Boaz's feelings and care for her? No; if she burns the toast or calls him a bad name, Boaz isn't going to kick her out. If she joins herself to another man, then all bets are off.
This is the way God treats you. God has redeemed you because he wants you. Mess up on a Tuesday? Not good, but not the end of the world either. Join yourself to another god? All bets are off.
But it gets even better! If you join yourself to another god and thereby separate yourself from God - and then change your mind and want to come home, God will let you!
Because he loves you.
Heard this before? Well yes, used in reference to Hosea and Gomer as a parallel to God's love for Israel. Israel is a model, type, or icon of the people of God. While the Hosea story is a corporate story, the principle is the same between you and God.
Really mess up bad? God still loves you and will take you back just as Hosea did for Gomer, and just as God did over and over again for Israel.
This January first, accept the reality of having been reconciled to God and live into that redemption. Don't sweat too much over the fact that you haven't been and don't think you can be perfect in the future. Yes, that is what God has called his bride to - faithfulness. But, God knows you're human and he really is prepared and has removed your sins as far as the east is from the west.
Lower your defenses and live "in Christ," to become the best image of God you were made to be.
Happy new year!