I. Evangelism is important because of the Nature of the Gospel. (vv. 21-23)
The first truth is that evangelism is important because of the nature of the gospel. We see this truth in vv. 21 – 23. There it says, “And he said to them, ‘Is a lamp brought in to be put under a basket, or under a bed, and not on a stand? For nothing is hidden except to be made manifest; nor is anything secret except to come to light. If anyone has ears to hear, let him hear.’” Jesus begins these verses by asking a question. Really, he asks two questions here. Some translations make it into one, but really there are two questions. Literally these questions could be translated, “A lamp is not brought out in order to be placed under a container or under a bed is it? Is it not brought out in order to be placed upon a lamp stand?” As we look at these questions it is clear that both of these questions are making the same point. That is, by its nature a lamp is not intended to be hidden. In fact, lamps are meant to give off as much light as possible. You would not take a lamp and put it under bowl, or hide it under your bed. If you were going to do that then you might as well not even have a lamp at all. You see, by its nature, the purpose of the lamp is to give off light. The best place for the lamp to be able to give off light is the lamp stand. So a lamp is not meant to be hidden! This is clear.
The reason why Jesus makes this point about the lamp is because the same thing is true about the gospel. The gospel is not meant to be hidden. The gospel is intended to save souls and reconcile men to God. In order for this to happen it must not be hidden. It must be displayed openly for everyone to see it. Thus, the illustration of the lamp is pretty simple to understand. Just as a lamp is not intended to be hidden, the gospel—by its nature—is not intended to be hidden. But with this in mind one cannot help but wonder why Jesus veiled the gospel. Remember, back in vv.11-12 Jesus made it clear that he spoke in a parables in order to veil (or hide) the gospel from the masses. In fact, the smaller “inner circle” was only able to understand the truth because the “secret” had been given to them. But why? Why was there a secret to begin with, and how does this secret match up with Jesus’ parable about the lamp? Well Jesus makes the connection clear in v. 22.
In v. 22 Jesus reminds us that the purpose of hiding something is to that it can later be revealed. This too is a pretty simple idea to understand. In fact, if you have ever hidden a Christmas present from your child then you understand this idea. But how does it apply to the “secret” about Jesus? Well, one commentator explained it this way:
[His disciples] must not think that He intended the revelation to them to remain a secret. The Kingdom of God, as embodied in Jesus’ Person and ministry, was now a veiled revelation to those without, but He intended that later it should receive a glorious manifestation through the ministry of His followers.
In other words, Jesus hid the secret so that it could later be revealed. When I first realized what Jesus was saying I had two questions. First, why did Jesus have to do this? Second, when would it finally be time for the gospel to be revealed? The answer to the first question is that Jesus had to allow himself to fulfill his earthly ministry. This meant that he had to weed out the people who were not truly interested in following him. Once he did this—by veiling the gospel—he was able to accomplish his ministry objectives, which included training his successors. With regard to the second question, in order for the full gospel message to be revealed Jesus had to first be crucified and resurrected. Only after these things happened could the full message be revealed. Thus, Jesus intended for his disciples to share this message with all, this why he left his disciples with the Great Commission in Matthew 25:168-20. Additionally, in Acts 1:8 we see that Jesus intended for his follower to take the message of the Gospel to the end of the earth.
So, even though Jesus had to veil his message while he was on this earth, this was only temporary. In Matthew 10:26-27 Jesus emphasizes this very point with these words:
So have no fear of them, for nothing is covered that will not be revealed, or hidden that will not be known. What I tell you in the dark, say in the light, and what you hear whispered, proclaim on the housetops.
By its nature, the gospel is intended to be “proclaimed on the roof tops.” We must never have an elitist attitude and seek to veil the gospel from those who do not believe. This is absolutely pivotal, and makes this clear in v. 23. This is a message with eternal significance, and whoever has the ears to hear the spiritual principle of this parable must listen. We must hear was this truth is and accept. We must submit to Jesus’ teaching in order to have a relationship with Him, and be a part of the Kingdom of God. We must hear this, we must perceive it, and we must act upon it. Evangelism is important because of the nature of the gospel.
 D. Edmond Hiebert, The Gospel According to Mark, 116.