Summary: A brief look at the forgiveness of sins, past, present, and future
In order to render a response to the question asked, it is vital to review the entirety of Scripture and not just verses extracted out of context.
Christians serve a God who is “rich in mercy” and continually proves His “great love for us.” He has made every Born-Again Christian “alive with Christ even when” they “were dead in transgressions.” It is by His grace that they “have been saved.” There is absolutely nothing they could ever do to be worthy of it. The wondrous heavenly Father has “seated” them “with him in the heavenly realms in Christ Jesus” (Eph. 2:4-6).
Mankind is now dead in their sins because of Adam. But in Jesus, they are made alive! To be “alive in Him” means that they are dead in their transgressions because it is "by His grace we have been saved" (Eph 2:5). It is only by His grace and not by anything they could ever do. Since they “have been raised with” Jesus, their life is now “hidden with Christ in God.” They must now set their “hearts on things above, where Christ is seated at the right hand of God” (Col. 3:1-3).
When a Born-Again Christian sins their justified position before God stays the same but their condition at that moment is changed. If a husband or wife hurts the other and does not apologize or repent of his or her mistake, their condition, or relationship, is harmed, even though they are still just as married as when they were in newly-wedded bliss. In the current legal system, the only way the behavior could change their position is if they both mutually agree to get a divorce.
"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." (1 John 2:1-2)
The intercession of Jesus assures them that they have forgiveness. "In the same way, the Spirit helps us in our weakness. We do not know what we ought to pray for, but the Spirit Himself intercedes for us with groans that words cannot express" (Rom 8:26).
When a Born-Again Christian sins, Jesus is always interceding on their behalf before God, the Father. Their relationship with Jesus is based upon what He has already done for them, not what they have done for Him.
“I give them ETERNAL life, and they shall NEVER perish; no one can snatch them out of my hand. My Father, who has given them to me, is greater than all; no one can snatch them out of my Father’s hand" (John 10:28).
In the past of the Born Again Christian “He chose" them "in him before the foundation of the world, that we should be holy and blameless before him. In love, he predestined us for adoption as sons through Jesus Christ (Eph 1:3-14) and sealed them with the promised Holy Spirit.
In the 'present' of the Born-Again Christian, they "have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, which he lavished upon us, in all wisdom and insight making known to us the mystery of his will, according to his purpose (Eph 1:7–9). If they are left in their sin, then they are separated from God. Only the single one-time sacrifice of Jesus can bring the holy God so close that He never leaves.
In the 'future' of the Born-Again Christian, the Holy Spirit is the guarantee of their "inheritance until" they "acquire possession of it, to the praise of his glory" (Eph 1:9–14).
When the Born-Again Christian confesses their sins, “He is faithful and righteous to forgive" their "sins and to cleanse" them "from all unrighteousness” (1 John 1:9).
God does not count their sins against them after they believe in Jesus Christ. They will never be condemned in the future. They were condemned before they believed in Jesus, but not after they believe. From a logical observation, Jesus died to forgive all sins in the past before anyone was born today, which would seem to indicate that He died for all future sins, including those that happen after a person becomes justified through conversion.
“Therefore there is now no condemnation for those who are in Christ Jesus.” (Rom. 8:1)
The Born-Again Christian is a "Good Tree" and they habitually walk in the light of God. A "Bad Tree" habitually walks in darkness, and they never had true fellowship with Jesus (Luke 6:43-45). The Born-Again Christian walks in the light, and they are cleansed from all sin and unrighteousness because they are filled with the righteousness of Jesus (Phil 1:1). The "Bad Tree" is NEVER cleansed from all sin because they have never confessed to committing sin before a Holy God, which is why Jesus says He NEVER knew them (See 1 John 1:5-2:6).