Anyone hearing the word doulos in New Testament times, would have thought "slave." That's how people would have understood doulos who were hearing it in that day. If you were a slave, you were owned. You had a master, an owner. He owned you. You would have forfeited your own personal rights. You would have been expected to obey everything the owner said. The slave-owner relationship is what describes the relationship of the believer, the saved person, to Jesus Christ.
When Jesus said that no man can serve two masters, He was saying that no man can be a slave to two owners. The servant of "well done thou good and faithful servant" is a slave. That's easy to see in the context. His owner is who says "well done" to him. Jesus doesn't become owner at some point into someone's salvation, but at the point a person believes. He believes that Jesus is his new Owner. Everyone is a slave to something. People who are saved became slaves to Jesus the moment they believed on Him.
Saved people are slaves to Jesus because He bought them. 1 Corinthians 7:22-23:
For he that is called in the Lord, being a servant, is the Lord's freeman: likewise also he that is called, being free, is Christ's servant. Ye are bought with a price; be not ye the servants of men.
A person who is "called" is saved. "The called" are always saved people. They are all His slaves. "Servant" here is doulos. They "are bought with a price" (also see 1 Cor 6:19). What was the price? It was the "precious blood of Jesus" (1 Peter 1:18-19).
The companion word to doulos in the New Testament is kurios. If you have a slave, you have an owner or lord. The lord owns. Kurios is found 717 times in the New Testament. You get these two words together in the same verse 47 times. Consider these:
Matthew 10:24, "The disciple is not above his master, nor the servant above his lord."
Matthew 24:45, "Who then is a faithful and wise servant, whom his lord hath made ruler over his household, to give them meat in due season?"
Luke 12:37, "Blessed are those servants, whom the lord when he cometh shall find watching: verily I say unto you, that he shall gird himself, and make them to sit down to meat, and will come forth and serve them."
John 13:16, "Verily, verily, I say unto you, The servant is not greater than his lord; neither he that is sent greater than he that sent him."
Acts 4:29, "And now, Lord, behold their threatenings: and grant unto thy servants, that with all boldness they may speak thy word."
2 Timothy 2:24, "And the servant of the Lord must not strive; but be gentle unto all men, apt to teach, patient."
Christians are called "slaves" all the way through the New Testament---apostles, pastors, and those with no office.
Jesus is Savior, no doubt. 37 times in the whole Bible do we have the word "Savior." The Greek word is soter. We have that word 23 times in the New Testament. How many times is the term "Savior" in Romans? Zero. It's once in John (4:42) and once in Acts (5:31). So Savior 23 times and Lord 717 times in the New Testament. How many times is kurios in Romans? 42 times. John? 53 times. The message written and preached by the Apostles is that "Jesus is Lord."
In the title, I said the anti-Lordship teaching is evil. And I mean anti-Lordship teaching regarding salvation. That's what Lordship teaching is about---salvation. If someone is to come to Christ, he must deny himself. He must relinquish self as Lord for Jesus as Lord. That means He must become a slave to Jesus. He recognizes that. Preachers shouldn't leave that out of the presentation.
No Lordship in "evangelistic" preaching is now standard fare, in part because of ant-Lordship teaching. It goes something like the following sample phraseology.
"If you ask Jesus to save you, He will."
"Ask Jesus to be your Savior and He will be."
"If you pray for Jesus to save you, He will."
"If you trust Jesus as your Savior, He'll save you."
"If you believe in Jesus as your Savior, He'll save you."
Those are now the norm in modern evangelistic methodology. You don't see Jesus or the Apostles do this at all. Nothing even remotely like it. It isn't a method derived from the Bible. It isn't of God. Try to find "as Savior" in Scripture---you won't find it; it isn't in there. Again, nothing even like it is in the Bible.
What's evil about the anti-Lordship teaching is that it is not at all in the Bible and yet it is presented like it is, totally misrepresenting God. It gives people a false presentation of salvation. It falls short of telling people Who Jesus is. It gives them a false impression about the relationship with Jesus that they are being invited to or are entering into. It offers salvation without revealing how to obtain that salvation.
Very often the incomplete and, therefore, false message exempt of Lordship perverts the teaching of Scripture even more so by also twisting the doctrine of sanctification. Professors of faith go on serving themselves, thinking they are saved, understanding that their disobedience is somehow justified by reality of some future date of dedication. They're saved, just not "dedicated." Jesus is Savior to them, but not quite Lord. At some later date, they might bump themselves up to that higher plateau of spiritual existence, perhaps when they get "revival." "Lordship" is just one of the steps of Christian growth. This too is evil.