Passage
And by this we will know that we are of the truth, and will assure our heart before Him
1 John 3:19 (LSB)
Nearby Context
1 John 3:17 But whoever has the world’s goods, and sees his brother in need and closes his heart against him, how does the love of God abide in him?
1 John 3:18 Little children, let us not love with word or with tongue, but in deed and truth.
1 John 3:19 And by this we will know that we are of the truth, and will assure our heart before Him
1 John 3:20 in whatever our heart condemns us; for God is greater than our heart and knows all things.
1 John 3:21 Beloved, if our heart does not condemn us, we have confidence before God;
Study Lenses
The verse centers on "truth", "assure", "heart", and "before". It is saying that the verse draws attention to "truth" and "assure", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 18's "Little children let us not love with..." into verse 20's "in whatever our heart condemns us for...", so "truth" and "assure" belong inside that flow. In 1 John context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "truth" and "assure" with trust shaped by these words, not by a vague optimism outside the passage.