The Greek words behind “gospel” and “evangelism” come from the same root. It’s easy to explain in Portuguese: “gospel” is evangelho and “evangelism” is evangelismo. You can’t have one without the other.
The English word “evangel,” for gospel, does exist, but nobody uses it. Maybe someone can start a campaign to revive it. Or, maybe better, start using “Good News” for gospel and “Good Newsism” for evangelism. Or maybe not.
The important thing is that we understand that evangelism is part and parcel of the gospel. You cannot be a defender, protector, and preserver of the gospel without being a proclaimer of it. If it isn’t shared, it isn’t gospel. If I don’t share it and teach it, I’m not being faithful to the God who gave it.