I know I believe in God, Jesus, and the Holy Spirit, the One God. You are taking the question, as if by not being catholic, I do not believe in Him.
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John 3:16
16 For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life.
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On the day of judgement, I know my fate, I know I cannot argue with God. I know I am guilty for I have broken God’s law, the commandments. I have lied, stolen, cursed, etc…
But Christ died for me, paying my debt with His Body and Blood, once and for all.
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Hebrews 10
11 And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins. 12 But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, 13 from that time waiting till His enemies are made His footstool. 14 For by one offering He has perfected forever those who are being sanctified.
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He offers this payment by grace (an undeserved gift), through faith
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eph 2:8-10
8 For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, 9 not of works, lest anyone should boast. 10 For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them.
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This payment is offered to those who repent (confess and forsake your sins) and believe (trust with all your heart) in the Lord Jesus.