If your ancestors were exclusively from Essex, I'm not sure that Ancestry or My Heritage will be of any more use than Family Search. (If they haven't got images of a county's records, these companies often use indexes that come from Family Search.)
Essex is a county that has chosen to digitise and host images of their record's in house rather than licencing them to one of the commercial companies.
Family Search does have some indexes to some Essex parishes. If you look at the page for Great Chesterford you'll see that they do have some records but what they have is 'undefined' so we don't know exactly what was and wasn't indexed.https://www.familysearch.org/wiki/en/Great_Chesterford,_Essex_Genealogy
If you click on Essex Ancestors it will take you to the Essex County Council site which is pay to view.(
If you click on FSPRS it will take you to the search page on Family Search for these 'records' ( caveats: we don't know what dates were indexed As an index any additional information in the original register won't be included. However, you can view images at an LDS history centre but there may not be one nearby)
Search Benjamin Barrett Great Chesterford and you'll find several entries including the 1683 marriage.Click on the entry and you'll see the details. Under information is 'citing this record' Cut and paste this citation to use under sources on the profile.
Although it hasn't got any transcripts for this particular parish, another free site called Freereg is often worth checking They try to add all the info from the original https://www.freereg.org.uk/
slight edit removing some information