Quick reply messaging from your Lock screen may be convenient, but it isn't secure.
With interactive notifications you can swipe left across any iMessage on the Lock screen and quickly send off a reply, no passcode, password, or Touch ID required. That's great if you're always in a rush and just need to answer everything and anything as fast as possible. It's not so great if you often leave your iPhone or iPad unattended, where other people can potentially reply to your messages either as a prank or maliciously. Interactive notifications are enabled by default, but if you'd rather have security than convenience, you can easily turn them off.
How to turn off quick reply messaging on the iOS Lock screen
Launch the Settings app on your iPhone or iPad running iOS 8 or higher.
Tap on Touch ID & Passcode.
Turn Off the option for Reply with Message.
How to turn of message previews on the Lock screen
If you want to make your messages even more private, you can also turn off Message previews altogether, which prevents people from reading texts and iMessages on your Lock screen. They can still see who sent the message, mind you, just not what the message says.