But know this, that in the last days grievous times shall come.
This know also, that in the last days perilous times shall come.
BUT UNDERSTAND this, that in the last days will come (set in) perilous times of great stress and trouble [hard to deal with and hard to bear].
Understand that the last days will be dangerous times.
And know this: that in the last days perilous times will press near.
Know also this, that, in the last days, shall come dangerous times.