Praying for the lost is a waste of time.

Some folks think that praying for the lost is a waste of time. This is especially true among Calvinists, who think God predestined us to be saved or damned, and nothing can change that, even the supplications of grandma to God. Then why did Paul pray for the lost Jews to be saved?

Brothers, my heart’s desire and prayer to God for the Israelites is that they may be saved. (Rom 10:1)

Some are going to refute this by saying the Jews were God’s chosen people to begin with. Yet the first few chapters of Romans condemns the Jews for their proud reliance on being God’s chosen people and relying on their ancestry from Abraham. (Romans 2 - 4)

Prayer alone won’t get the job done, however. All the prayers in the world won’t lead anyone to salvation unless they hear the word of God being preached. Note:

We sat down and began to speak to the women who had gathered there. One of those listening was a woman named Lydia, a dealer in purple cloth from the city of Thyatira, who was a worshiper of God. (Emphasis mine) The Lord opened her heart to respond to Paul’s message. (Acts 16:13-14)

Lydia worshiped God but she was not saved. That said, all the preaching in the world won't change a hard heart. This is where behavior, rather than preaching, becomes a testimony. Note:

Wives, in the same way, be submissive to your husbands so that, if any of them do not believe the word, they may be won over without words by the behavior of their wives, when they see the purity and reverence of your lives. (1 Peter 3:1-2)

Unfortunately, there are many Christians who do nothing but pray, never realizing that they are God’s instrument for spreading the Good News. They prefer prayer to preaching. Peter is dealing with the close relationship between a husband and wife, not your once-a-month fishing trip buddies. Behavior is effective, but there eventually comes a time when you have to lay it out for your buddies. Or else you don’t care about someone, and are letting them go blindly into eternity. This lack of concern is addressed in the book of Ezekiel:

I have made you a watchman for the house of Israel; so hear the word I speak and give them warning from me. When I say to the wicked, “O wicked man, you will surely die,” and you do not speak out to dissuade him from his ways, that wicked man will die for his sin, and I will hold you accountable for his blood. But if you do warn the wicked man to turn from his ways and he does not do so, he will die for his sin, but you will have saved yourself. (Ezek 33:7-9)