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Forgiveness of sins is only available to those who believe the gospel, repent and are baptised by immersion into Christ.
Acts 2:37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do? 38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins...
At baptism all our former sins are washed away and after baptism we are required to live by the commandments of Christ.
John 15:13 Greater love hath no man than this, that a man lay down his life for his friends.
14 Ye are my friends, if ye do whatsoever I command you.
We will still sin but in Christ we can have our sins forgiven if we confess them in prayer.
1 John 1:7 But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin.
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
1 John 2:1 My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
In theory, all sins, save blasphemy against the Holy Spirit (which we cannot commit, because the powers are not available today), if repented of, can be forgiven.
Mark 3:28 Verily I say unto you, All sins shall be forgiven unto the sons of men, and blasphemies wherewith soever they shall blaspheme: 29 But he that shall blaspheme against the Holy Ghost hath never forgiveness, but is in danger of eternal damnation:
However, if after baptism we deliberately continue in our previous sinful ways we will not be forgiven.
Hebrews 10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
If we refuse to forgive those that sin against us we will not be forgiven.
Matthew 6:15 But if ye forgive not men their trespasses, neither will your Father forgive your trespasses.
Confession is made to God in prayer through the mediation of Christ. No one else can mediate between us and God.
1 Timothy 2:5 For there is one God, and one mediator between God and men, the man Christ Jesus;
If we are baptised into Christ we join a body of believers who should pray one for another.
James 5:16 Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much.
Prayers of other baptised believers can help, but the splitting of a congregation into ‘clergy’ and ‘laity’ is false religion.
I hope this helps.