Jesus invites a people who were loaded and oppressed with religious ceremonies and formalities to find in Him the rest that they long for. There is an exchange of yokes, an exchange of labor and burdens. Those without Christ carry a heavy load of sin. They are under a hard taskmaster. Whether they know it or not, they have a harder road ahead and if they continue in that path the end of that road is one of eternal misery. When we come to Christ, by faith, we exchange our guilt laden yokes of bondage for His yoke of freedom. A yoke is symbolic of restraint. Christians are given true freedom and joy, but freedom is not liberty to do whatever a person feels like doing, it is freedom to love God and serve Him (see Romans 6:16-17). Christians do not take liberties because of their liberty (see Romans 6:1; 1 Corinthians 8:9). A disciple therefore is one who operates under the yoke that is placed upon Him by Christ.
A disciple is one who gladly takes on the yoke that Christ offers. What is his yoke? I am not so sure, I would say that it is all the duties that accompany the profession of being a Christian; the responsibility of obeying all that Christ commands. Whatever it is, it certainly isn't "burdensome" or "grievous" (1 John 5:3). Jesus says "learn of me" and a disciple is a learner. When Christ said that He is "meek and lowly in heart" He wasn't bragging. He was simply declaring truth about His person. This is humble confidence. In fact, this is a statement that verifies Jesus as Messiah in Zec. 9:9. It is Christ who is the pattern. The example to follow. Once again, a disciple strives to be like his master, and so every disciple of Christ, is called to be like Christ in their very character.