My take on this:
- he was ordered to wrap it up, having conclusively proven Russia interfered with the election
- there is some very damning info in the report that will be redacted re: collusion but no one is on record admitting there was an agreement to do such and such if Trump won, etc
- these are accomplished liars and Trump did not personally testify so was not implicated (had he testified in person things would be very different)
The “real report” is going to read differently than Barr's summary but will be heavily redacted. Policies against making public any info about unindicted subjects will shield Trump and his family from direct implication and this is just intended to appease him and his base. The rest of the world will know what happened and the real story will slowly emerge but this summary, “no collusion”, will be what people remember and is all Trump's supporters will ever hear about.
EDIT 2019-03-26 – Rod Rosenstein Didn’t Even Clear Trump on All the Topics He Hired Mueller to Investigate – In this interesting analysis Marcy Wheeler explains that Barr's summary side-stepped one of the three objectives of the investigation... Why?