that you may be blameless and innocent, children of God without blemish in the midst of a crooked and twisted generation, among whom you shine as lights in the world, (Philippians 2:15, ESV)Don't grumble or dispute was the command in the previous verse. If for no other reason, we ought not to do that, simply because God has commanded that we not do that. But here we can see one of the glorious benefits of avoiding the grumbling: when grumbling is absent, we get to shine!
Think about it this way: When we share the glorious gospel of Jesus Christ, we are sharing something that ought to surpass any and every bad thing that we may encounter here. God has made a way for us to get to know him, and it is completely separate from our ability to accomplish this. He didn't just pave the way to salvation, He IS the salvation. ... God Saves People! He saves them from their sin, he saves them from the power of sin, he saves them from the penalty of sin, and he grants them the good favor that his one and only Son deserves. He accomplished all of this good grace while continuing to be absolutely just and righteous. His son, Jesus Christ, bore all of the wrath of God on our behalf. What more could we ask for?!?
How can we show the glorious nature of what we are recipients of, if the little things of this life (or the big things of this life), bog us down in such a way that we walk around grumbling and disputing like the rest of the world?
Your glorious acceptance of the course of this life will speak to the glorious nature of the great gift you have received in salvation. This world is crooked and twisted, but if you can walk around blameless and innocent... Children of God... You will shine as lights in this dark world.
And many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt. And those who are wise shall shine like the brightness of the sky above; and those who turn many to righteousness, like the stars forever and ever. (Daniel 12:2-3, ESV)