What does the Bible say about preaching the gospel as a free gift?

In Matthew 10:7-8, Jesus instructs His disciples to freely give what they have received, emphasizing that the gospel is a gift of God's grace without any charge or obligations. True preaching involves proclaiming the specific message of Christ and Him crucified, as this is the source of salvation for all believers. Preachers are not to place conditions on receiving the gospel, nor should they seek financial gain through their ministry. The essence of preaching is to declare the kingdom of heaven, which is the free offer of salvation through Christ.