God is patient. He is so patient that sometimes we mistakenly accuse Him of being unjust. He is patient, but He is also just (Deuteronomy 32:4).
Justice means getting what you deserve. So … what do you deserve from God?
The Bible says that you deserve eternal punishment for your sins against Him. The soul that sins shall die (Ezekiel 18:4, 20). The wages of sin is death (Romans 6:23).
In His mercy, God sent His beloved Son to take the wages we deserve through His death on the cross. This way, since His justice fell upon His own Son, the Father can bestow the gift of mercy upon us. It was an unfair, but a just trade.
How then, does one receive God’s mercy instead of wrath? By trusting that Jesus did everything necessary for you to receive eternal life. You can add nothing to what Jesus did in your place.
In Christ Jesus, God set forth His Son as a payment in full through His blood, through faith, to prove His justice. In His patience, God passed over the sins that were previously committed to prove in the present time His righteousness, so that He might be both just and the justifier of the one who has faith in Jesus (Romans 3:25-26).