Mosiah 4:28

And I would that ye should remember, that whosoever among you borroweth of his neighbor should return the thing that he borroweth, according as he doth agree, or else thou shalt commit sin; and perhaps thou shalt cause thy neighbor to commit sin also.

Reference:

Searching the Topical Guide for scriptures related to Honesty

What is the scriptural or historical context of this scripture:

King Benjamin is teaching the people from his tower. He teaches advanced obedience concepts of following the gospel plan. He is such a good teacher that all of his people feel the spirit and desire to follow his example.

Thoughts about this scripture:

King Benjamin uses a simple example here of borrowing something from a neighbor. But he doesn't just lay the requirement of returning that which was borrowed on us, he also says that if commit the sin of not returning that which we borrow we may cause our neighbor to commit sin.

This doesn't absolve our neighbor of that sin, but we do not escape responsibility for it either. When we provide fodder for gossip, seeds of anger, and potentially testimony weakening examples to others we must feel the guilt of that as well.

How does this strengthen my testimony

I love the scriptures. In them we find the basic principles that start our testimony and begin our journey to return to Heavenly Father. But we also find advanced concepts and wisdom. As I continue to study the scriptures, I find teachings that I hadn't noticed before. Then my understanding of the gospel and of God and of the world around me deepens. And my love of the scriptures and of God grows.