The Lord's elaboration on "disputations" and "contentions" is important and consistent enough that all 3 verses should be considered together.
First, He clarifies that baptism must be done as He "commanded you." Deviations are not permitted and should not be asked for, or entertained. That is the thing about ordinances. When given, they are to be kept in exactly the manner they come from Him. When we change them we risk breaking the covenant between Him and ourselves. (Isa. 24: 5.)
The Book of Mormon is silent about the "disputations" which existed among them over baptism. However, when Christ says there has "hitherto been" disputes, we know they existed. It becomes apparent from later passages that one practice which caused some of the argument was the issue of baptizing infants. There were likely others, as well. The Lord wants that to end. Perform the ordinances as He sets them out, and stop arguing about the manner.
The reason arguments arise is because men stop gathering light by righteous behavior. When they lose light they cease to understand the truth. They stray from the correct practice of the ordinance because they are unable to understand its importance. They see no reason to continue the ordinance in one form when another seems to work just as well. The result is a change to the ordinance. It is ever the same. By the time the change is made, the ones making it are unaware of any importance associated with the ordinance they change. They discard what they view is meaningless. It would require a good deal more light and truth for them to understand the importance of what was given them. But that light and truth has passed away from them because of their conduct.
Into the darkness the devil enters with arguments over the ordinances: Why do it that way? It really doesn't mean anything. It is arcane and outdated. It doesn't really matter as long as you still have faith in Christ. [That particular lie is very effective because it allows the person to presume they have faith, when in fact they haven't the faith sufficient to obey Christ.] People will get more out of the changes if we make them. People will have greater peace of mind if we baptize their infants. We'll save more souls, because by baptizing them when they're infants we include everyone who would die before getting baptized. Our numbers will increase. We'll look more successful by getting more followers by adding their numbers into the group. What we change isn't important, anyway. If it were important, we would know that, and since it doesn't seem important to us, it must, in fact, not be important. Those who rebel at change are not really faithful. This shows inspiration; it's faith affirming. Change is proof that God is still leading us. ...And other such arguments and persuasions from our adversary.
On the other hand, Christ is saying to keep the ordinances unchanged. And further, don't even begin to dispute them. They are off limits for argument, dispute and discussion. When you open the opportunity to dispute over the ordinances, you are allowing the devil an opportunity to influence the discussion and change the ordinances.
Disputes lead to contention, contention leads to anger, and anger is the devil's tool. So don't start down that road. Accept and understand the ordinances. If you are perplexed by them, then let those who understand speak, exhort, expound and teach concerning them. As they do, you will come into the unity of faith and become one. Perplexity cannot exist when there is light and truth. Light and truth comes from understanding the ordinances, not changing them. So do not begin the process through dispute. The purpose of discussion is not to dispute, which leads to contention, which leads to anger.
When the Gospel and its ordinances turn into something angry and contentious, then the Spirit has fled, and souls are lost. It is the devil's objective to prevent you from practicing the ordinances in the correct manner. But, more importantly, it is his objective to prevent you from becoming one. When he uses arguments over ordinances to cause disunity, he is playing with two tools at the same time. First, changing the ordinances brings about cursings, and second, encouraging contention and anger grieves the Spirit, and prevents the Saints from becoming one.
As a result, disputes or discussions over ordinances, which could lead to changing them, should not be entertained. As soon as the ordinances are open to dispute, reconsideration, alteration or to being changed, then you are opening the door to this whole process. It culminates in the souls of men being lost through apostasy. Once the ordinances are changed, the earth is cursed (Isa. 24: 5) and Israel is scattered rather than gathered (Jere. 31: 36).
The devil knows this, even if men do not. Men are urged to take steps they presume have little effect, all the while being lied to by the enemy of their souls.
When men arrive at the point they are angry in their hearts with one another, they are not united by love as they are intended to be. These are the end results of the two paths. One leading to love and joy (Hel. 5: 44), and the other to anger and wrath (D&C 76: 33).
Disputes over ordinances are caused by the devil. Ordinances that preserve symbolic truths and have the power to save are turned into tools for the devil by disputations. It is a complete victory when discussions about changing ordinances are allowed to take place. Even good men are taken in by such disputes.