Mark 16:
17 And these signs shall follow them that believe; In my name shall they
cast out devils; they shall speak with new tongues;
18 They shall take up serpents; and if they drink any deadly thing, it shall
not hurt them; they shall lay hands on the sick, and they shall recover.
You can understand it by cross referencing to Matthew 10:5-8
5 These twelve Jesus sent forth, and commanded them, saying,
Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not:
6 But go rather to the lost sheep of the house of Israel.
7 And as ye go, preach, saying,
The kingdom of heaven is at hand.
8
Heal the sick, cleanse the lepers, raise the dead, cast out devils: freely ye have received, freely give.
Preaching of the gospel of the kingdom to Israel, always required signs and wonders.
The nation Israel, ever since Moses first appeared to them in Exodus 4, required signs and wonders if you want them to believe that you are sent by God to them.
So if the 11 were to continue preaching the gospel of the kingdom to the nation Israel, Jesus provided signs for them to authenticate their spoken word, which was also confirmed by the final verse in Mark
20 And they went forth, and preached every where, the Lord working with them, and
confirming the word with signs following. Amen.
The Apostle Paul tells us in the Body of Christ what Jews required in 1 Corinthians 1:22
For the Jews require a sign, and the Greeks seek after wisdom
But for now, the nation Israel has now fallen, and the gospel of the kingdom no longer saves anyone today.
Today, we preach the gospel of the grace of God, summed up by Apostle Paul in 1 Corinthians 15:1-4. Signs and wonders are no longer part of this gospel, so we should not take Mark 16:17-18 as a guide for us.
We walked by faith and not by sight 2 Corinthians 5:7