Sins are not graded in the Bible. Sin is the breaking of any one of God’s commandments. All and any sin brings us under the sentence of death.
Ezekiel 18:4... the soul that sinneth, it shall die.
Romans 6:23... For the wages of sin is death;
We might suppose that murder is a greater sin than robbery, but in reality death is the sentence for both.
Romans 5:12 Wherefore, as by one man (Adam) sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
On the positive side, all sins, except blasphemy against the Holy Spirit, (which we are unlikely to commit) can be forgiven in Christ.
Matthew 12:31 Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Spirit shall not be forgiven unto men. 32 And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Spirit, it shall not be forgiven him, neither in this world, neither in the world to come.
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 Spirit hath never forgiveness, but is in danger of eternal damnation (condemnation): 30 Because they said, He hath an unclean spirit.
If we want forgiveness for sin we must first of all believe that Jesus was provided by God to take away our sin.
John 8:24 I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am he, ye shall die in your sins.
If we die without forgiveness of sins we die without hope and perish. If we believe the gospel and are baptised into Christ all our past sins are washed away.
Mark 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned (condemned).
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...
Acts 22:16 And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
With baptism we begin a new life in Christ, living by his commandments. We will still sin but we can have forgiveness for our sins if we confess them in prayer.
1 John 1:7... 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.
This is not to say that we can commit sin on purpose on the presumption that God will forgive us. Neither can we defer baptism and continue in sin. God knows our hearts and will judge us accordingly.
Romans 6:1 What shall we say then? Shall we continue in sin, that grace may abound? 2 God forbid. How shall we, that are dead to sin, live any longer therein? 3 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? 4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:
2 Corinthians 7:1 Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
I hope you have found this helpful.