The word "it's" is a contraction of it and is. "Its" is the neuter version of his or her.its not part of gods plan
The word "God" is a proper noun. As such, it should be capitalized.
A noun is possessive if a phrase can be changed to say that an item belongs to someone. In other words, the plan of God becomes "God's plan".
It's God's plan for you to quit trolling the tread for replies, Mr. Troll.
You're welcome. ;-)