1 JOHN 3:19-3:24

By this we shall know that we are of the truth and reassure our heart before him; for whenever our heart condemns us, God is greater than our heart, and he knows everything. Beloved, if our heart does not condemn us, we have confidence before God; and whatever we ask we receive from him, because we keep his commandments and do what pleases him. 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 3:19-24

ASSURANCE FOR A WAVERING HEART (v. 19-22)

The heart is deceitful above all things, and desperately sick; who can understand it? “I the Lord search the heart and test the mind, to give everyman according to his ways, according to the fruit of his deeds. —JEREMIAH 17:9-10
Who shall bring any charge against God’s elect? It is God who justifies. If God declares you righteous by faith in Christ, who can overturn God’s verdict? —ROMANS 8:33
“Search me, O God, and know my heart! Try me and know my thoughts! And see if there be any grievous way in me and lead me in the way everlasting!” —PSALM 139:23-24
“Lord, you know everything; you know that I love you.” —JOHN 21:17
Let us then with confidence draw near to the throne of grace, that we may receive mercy and find grace to help in time of need. —HEBREWS 4:16
We have confidence to enter the holy places by the blood of Jesus. —HEBREWS 10:19
And whatever we ask we receive from him, because we keep his commandments and do what pleases him. —1 JOHN 3:22

THE GROUNDS OF OUR ASSURANCE (v. 23-24)

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. —1 JOHN 3:23
If you confess with your mouth that Jesus is Lord, and believe in your heart that God has raised him from the dead, you will be saved. —ROMANS 10:9
For everyone who calls on the name of the Lord will be saved. —ROMANS 10:13

The gospel is not only something to be BELIEVED, but something to be OBEYED.

But these are written so that you may believe that Jesus Christ, the Son of God, and that by believing you may have life in his name. —JOHN 20:31
“I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing.” —JOHN 15:5
For you did not receive the spirit of slavery to fall back into fear, but you have received the Spirit of adoption as sons, by whom we cry, “Abba! Father!” The spirit himself bears witness with our spirit that we are the children of God, and if children, then heirs – heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also with him. —ROMANS 8:15-17