Through His Spirit
Matthew 10:20 says that when we are persecuted and bought to trial because of Jesus, we are not to worry about what to say because The Fathers spirit will speak through us.
Jesus said in John 14:25-27, ‘All this I have spoken while still with you. But the advocate, the Holy Spirit, whom the Father will send in my name, will teach you all things and will remind you of everything I have said to you. Peace I leave with you; my peace I give you. I do not give to you as the world gives. Do not let your hearts be troubles and do not be afraid.
see also, judges 6:34, and 1samuel 10:10. There are many more scriptures.
Through dreams and visions
Joseph had a dream sent by God. (Genesis 37). The king had dreams which disturbed him and only Joseph could explain them because they were from God. (Genesis 41)
Numbers 12:6 God said to the people, ‘Where there is a prophet among you, I the Lord will reveal myself to them in visions, I will speak to them in dreams.’
Joel 2:28 & Acts 2:17 say “In the last days, says God, I will pour out my Spirit on all people. Your sons and daughters will prophesy, your young men will see visions, your old men will dream dreams.”
Through his word, his Son, Jesus Christ.
John 20:30 Says ‘Jesus performed many other signs in the presence of his disciples, which are not recorded in this book. But these are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.’
The bible was written so that the message may be passed down from generation to generation so that many could be saved. And the ancient scrolls found, have mostly upheld the scriptures as they are now which gives us hope that the people who have re-written them over the centuries did their best to translate it truthfully, to the best of their ability. Indeed the last paragraph in the last book of the bible says, ‘I warn anyone who hears the words of the prophesy of this scroll: If anyone adds anything to them , God will add to that person the plagues described in this scroll. And if anyone takes words away from this scroll of prophecy, God will take away from that person any share in the tree of life and in the Holy City, which are described in this scroll.'
He who testifies to these things says, “Yes, I am coming soon.”’
We have to be aware, though, that some dreams and visions do not come from God, but are deceptions of the devil or our own desires, so we should test them, by the bible, by our consciences and sometimes by asking God for confirmation, as in Judges 6:34.
Generally though, I would say, if anyone has dreams etc which tell them to harm someone, it is not from God, because he has done all that is needed through Jesus Christ on the cross – that was the whole point of the cross! He does not need our help to punish the wicked, they do it for themselves by rejecting Jesus and going their own way, so that when the end comes, they will not be saved from the destruction of the world.
This is how I understand my God. Read for yourself, see what you think.