And this is his commandment, that we believe in the name of his Son Jesus Christ and love one another, just as he has commanded us. Whoever keeps his commandments abides in God, and God in him. And by this we know that he abides in us, by the Spirit whom he has given us. (1 John 3:23-24 ESV)
Are you lacking in the assurance of your salvation? Take a close look at this verse.
1. Believe in the name of Jesus Christ
2. Love others
When you think about it, these two things encompass both tables of the Ten Commandments. The first four commandments deal with our relationship to God and the last six deal with how we love other people.
Of course one needs to guard against doing all the outward things listed in the Ten Commandments as a way to earn one's way into heaven. A heart changed by God will begin to conform itself to these commandments as a natural outcome. So if you are lacking assurance of salvation, look first to Jesus Christ for forgiveness of sin. Get that right and the rest will begin to flow as a result of God's work in your heart.