Is today's Christians' belief in water baptism (Matt 28:19) the reason they can't keep His commandment (I Thess 5:21; KJV) unbelief in POWER?

STOP PRETENDING TO BE CHRISTIAN!!!!!!!!!!

It was always water baptism and only pretend Christian sect and cult followers deny that!

When you reach eternity ask your mater Satan to explain your mistakes!

Read Mt. 28:19. Do you see the word "water" there? Or are you simply making an assumption here? In case you didn't know, assumptions lead to deceptions. 

Then, you reference "HIS" commandment with 1 Thess 5:21, which is a statement made by the apostle Paul to prove all things.  

So, how does baptism in Mt. 28:19 relate to what Paul wrote in 1 Thess 5:21 to prove all things?

I'll tell you how you cannot prove all things.... by using this sort of Assumptive Reasoning.

A person proves all things by verifying claims with Scripture; said to be in Scripture the inspired Word of God, by using a proper hermeneutic.

We don't "believe in" water baptism. We understand that it is necessary and has a specific purpose.

Water immersion baptism actually has an in-depth meaning. Consider the words given to John the Baptist when he was hesitant to baptize the Lord Jesus:

"Permit it to be so now: for thus it is fitting for us to fulfill all righteousness." (Matt. 3:15).

What did the Lord Jesus mean when he said “fulfill all righteousness”?

In Exodus 40:12-13 we read: Then you shall bring Aaron and his sons to the door of the tabernacle of meeting, and wash them with water. You shall put the holy garments on Aaron, and anoint him, and sanctify him, that he may minister to Me as priest.

The Lord Jesus Christ Himself, in order to minister as the faithful high Priest in the priest’s office, needed to be washed by the baptism of water (Heb. 2:17; 4:15; 5:5). If the Lord needed to do so, how much more then do believers need to do so? In 1 Peter 2:9, it is written, But you are a chosen generation, a royal priesthood, an holy nation, His own special people (Ex. 19:6; Rev. 1:6). The believer, without a doubt, needs to be water immersion baptized, so that like the priest standing in the priest’s office he can offer spiritual sacrifices to God (Heb. 13:15; 1 Pet. 2:5).