What was the reason behind Messi's suspension?
Reason behind Messi's suspension as per statement from FIFA is "directing insulting words at an assistant referee".
The FIFA Disciplinary Committee – in application of articles 77 a) and 108 of the FIFA Disciplinary Code (FDC) – has reached a decision in relation to the case of Lionel Messi following an incident that occurred during the match between Argentina and Chile on 23 March 2017 as part of the qualifying competition for the 2018 FIFA World Cup Russia™:
Lionel Messi has been found guilty of violating art. 57 of the FDC for having directed insulting words at an assistant referee.
As a result, Messi will be suspended for four official matches and sanctioned with a fine of CHF 10,000. The first match for which the sanction will apply is the next fixture in the preliminary competition of the 2018 FIFA World Cup Russia™ between Bolivia and Argentina, which will be played today, 28 March. The remainder of the sanction will be served over Argentina’s subsequent FIFA World Cup qualifying matches.
This article from Sun states Messi is being accused of saying, (contains foul language)
“f*** off, your mother’s a c***” to a match official
And this article from Mirror states,
Messi, 29, was furious with official Dewson Silva during the first half of the 1-0 victory, and was seen on camera verbally abusing Silva, reportedly declaring: (contains foul language)
“f*** off, the c*** of your mother."