What is a git commit object? How is it read?

When a project repository is initialized to be a git repository, git stores all its metadata in a hidden folder “.git” under the project root directory.
Git repository is a collection of objects. 

Git has 4 types of objects – blobs, trees, tags, and commits.

Every commit creates a new commit object with a unique SHA-1 hash_id.
Each commit object has a pointer reference to the tree object, its parent object, author, COMMITTER and the commit message.

Diagram: Single Commit object

To see the commit log message along with the textual diff of the code, run:
git show <commit_id>

Divya1@Divya:initialRepo [master] $git show f9354cb commit f9354cb08d91e80cabafd5b54d466b6055eb2927 Author: divya bhushan <divya_bhushan@hotmail.com> Date:   MON Feb 11 23:39:24 2019 +0100     Add database logs. diff --git a/logs/db.log b/logs/db.log new file mode 100644 INDEX 0000000..f8854b0 --- /dev/null +++ b/logs/db.log -0,0 +1 +database logs

To read a commit object git has ‘git cat-file’ utility.

Divya1@Divya:initialRepo [master] $git cat-file -p f9354cb tree 2a85825b8d20918350cc316513edd9cc289f8349 parent 30760c59d661e129329acfba7e20c899d0d7d199 author divya bhushan <divya_bhushan@hotmail.com> 1549924764 +0100 committer divya bhushan <divya_bhushan@hotmail.com> 1549924764 +0100  Add database logs.

A tree object is LIKE an OS directory that stores references to other directories and FILES (blob type).

Divya1@Divya:initialRepo [master] $git cat-file -p 2a85825b8d20918350cc316513edd9cc289f8349 100755 blob 054acd444517ad5a0c1e46d8eff925e061edf46c README.md 040000 tree dfe42cbaf87e6a56b51dab97fc51ecedfc969f39 code 100644 blob e08d4579f39808f3e2830b5da8ac155f87c0621c dockerfile 040000 tree 014e65a65532dc16a6d50e0d153c222a12df4742   logs