Did you know that you can have an assurance of salvation to know that you will live with God in eternity (Hebrews 11:1)? God tells us how that is done in His gospel -- the good news of salvation (Romans 1:16-17). There are many different gospels and denominations in evangelical Christianity, but there is only one way to be saved -- that is by the gospel of Jesus Christ (Galatians 1:6-8).
Christ's gospel is the good news that Jesus Christ interceded for us and received the punishment for our sins instead of us (Romans 5:9-11). He calls us to believe, repent and surrender to Him as Lord. He calls us to walk in obedience to Him. He wants to be more than Savior; He wants to be Lord and Master in your life (Acts 2:36).
It is only by His mercy and by His grace that any person can have a true assurance of salvation -- by grace alone, through Christ alone.