If you can't do anything else, maybe you can serve as a bad example. Here's a story of a bad example in evangelism.
The Old Testament reading for Pentecost 20 is the introduction to the story of Ruth in Ruth 1. The story introduces us to Jesus' ancestor in the faith, and is also an example of one of the non "physical Israel" saints in the OT. (Ruth was a Moabite. Other examples in the OT are Uriah the Hittite, the faithful general who was murdered by King David, as well as the saints in Ninevah, recounted in Jonah).
What I want to focus on is not Ruth, but Naomi, her mother-in-law. Naomi (whose name means "pleasant") is the bad example. We read of Naomi's very bad times: her husband's death, and the deaths of her 2 sons.
We can look at Naomi from 2 perspectives. First, she deserves genuine sympathy, suffering through what is a horrible situation. But her reaction is not good. I would do no better, but while we are encouraged to patience in such sufferings, Naomi shows none of that. Instead, she whines, complains, and reviles against God, saying that God has "afflicted" her (1.21). She further encourages her 2 daughters-in-law to abandon the true faith, and return to their ancestral idol worship (1.15). Naomi is at least partly "successful" in her negative evangelism: her daughter-in-law Orpah leaves Naomi, and the faith.
But someone has done something right here. Perhaps Naomi or her husband or her sons, but someone has taught her daughters-in-law (especially Ruth) about the true God. Even Naomi here -- in her bitterness -- blesses Orpah and Ruth, asking that the Lord would "deal kindly with you" (1.8).
We sin daily, and our efforts at sharing our faith fail, often miserably. But God's word does not fail. That's the message of Isaiah 55, that God's word does what it sets out to do, in spite of our failures to say the word rightly.
Should we be kind, winsome, patient, longsuffering? Absolutely. And will we fail to do that? Definitely. Like St. Naomi, we will speak the word badly at times. And like her, we live under the forgiveness that the Savior promises.
The second reading for Pentecost 20 is from 2 Timothy 2. That passage closes with this promise that Naomi in glory clings to, even as we do: God abides faithful. He cannot deny Himself. (2.13).