One of many ways modern Christians tend to water down the Gospel is to frame it as a mere invitation from God to come to Heaven. Or worse, we tell people to ask Jesus into their hearts. In some ways, this is accurate. As sinners, Heaven is a privilege God certainly doesn't owe us, and to ask Jesus in can be a sign of humility. However, this does leave out one crucial aspect of the message.
See, the thing about an invitation is there aren't really any consequences of saying no. If I invite you to my birthday party and you don't show up, you might not get an invite next time, but it's not like I can have you arrested and sentenced to life in jail. Contrast this with refusing to accept the Gospel. There are absolutely consequences for rejecting this invitation. God commands all people to repent. Not just "you are invited to repent, but it's cool if you don't". It is an explicit command. If one refuses this invitation, the consequences aren't simply missing out on a good thing. If one refuses the invitation to Heaven, the only alternative is an eternal stretch in Hell.
My brethren, this is not an invitation. We need to stop treating it like it's optional. When we spread the Gospel, we need to clearly articulate, as clearly as the Lord empowers us, exactly where people stand with God. Specifically, we stand before Him as defendants before a perfect judge. And we are most definitely guilty as charged. We are offered the chance to accept a full pardon at the expense of Christ. If we refuse that offer, it's conviction for us. Therefore, we are commanded to repent. Refusal to do so is sin in itself.