We belong to God through entering into the New Covenant. The New Covenant is eternal and everlasting full of blessing and rich promises. What does covenant mean? The dictionary describes it this way: a written agreement or promise usually under seal between two or more parties especially for the performance of some action. For it to be binding both parties must live by it and when we fail to maintain our personal relationship with God and choose to practice willful sin we are not living or abiding in the New Covenant terms.
Jesus lays out the terms and conditions of the New Covenant in John 15:1-10, note that they are Living. We enter the New Covenant through (active) faith in Jesus Christ, and we sign it, by our (active) obedience. The handshake so to speak is our baptism and the filling of His Holy Spirit in us. God gives this to us as His token of His promise (2 Cor 1:21-22) and so we may live up to our end.
God wishes that none would perish and He continually extends to all His grace. Though we may grieve His Spirit and even quench it we can count on His faithfulness. No matter what sin we have done and however long we have done it – He will not forsake us when we turn back to Him with a heart of repentance and we will be restored to Him in our relationship and standing.
But know this, if we do go on willfully sinning:
For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. Anyone who has rejected Moses’ law dies without mercy on the testimony of two or three witnesses. Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace? For we know Him who said, “Vengeance is Mine, I will repay,” says the Lord. And again, “The Lord will judge His people.” It is a fearful thing to fall into the hands of the living God. Heb 10:26-31