Mark 16:15

"Go into all the world and preach the gospel to all creation."

This divine commission (v.15-19) has its parallel in Matt. 28:18-20, Luke 24:47-49 and Acts 1:2-9, and must be understood by harmonizing these three accounts.

Christ indicates his authority:

"All authority has been given to me..." (Matt. 28:18).

"After He had by the Holy Spirit given orders to the Apostles" (Acts 1:2).

Preach to all creation:

Mark 16:15 (above), Luke 24:47 "to all nations".

"Make disciples of all the nations" (Matt. 28:19).

"You shall be my witnesses... to the remotest part of the earth" (Acts 1:8).

Baptize those who believe:

"He who has believed and has been baptized shall be saved" (Mark 16:16). (cf. Luke 24:47).

"Baptizing them in the name of the Father and the Son and the Holy Spirit" (Matt. 28:19).

"You shall be baptized with the Holy Spirit" (Acts 1:5)

"Lo I am with you all the days" (Matt. 28:20).

"These signs will accompany those who have believed" (Mark 16:17).

"I am sending forth the promise of my Father upon you" (Luke 24:49).

"You shall receive power when the Holy Spirit has come upon you" (Acts 1:8).

"Jesus . . . was received up into heaven" (Mark 16:19).

"He was lifted up while they were looking on" (Acts 1:9).

"He parted from them" (Luke 24:54)

The Apostles fulfilled that command as the following verses show:

"And they went forth, and preached everywhere, while₁ the Lord worked with them, and confirmed the word by the signs that followed" (Mark 16:20).

"the gospel… was ("has been" RSV) proclaimed in all creation" (Col. 1:23). cf. Heb. 2:3,4 and Acts of the Apostles.

CONCLUSION
It is obvious that Mark 16:19 has happened and will not be repeated. Since v. 16-18 are within the context of and directly related to verses 15 and 20, there may be no other valid conclusion than that they were fulfilled by the Apostles, because the commission was to them only, not to general believers.
There are, however, other verses which indicate to us the necessity of baptism, (e.g. Gal. 3:27).

Mark 16:17

"And these signs will accompany those who have believed" cf. previous notes on v.15.

These verses prove more than modern claimants desire because where is the person today who can perform the "signs" of v.18?

The gifts of the Holy Spirit were given to the Apostles in their fulness (so that they could spread the gospel throughout the whole world) but generally only individual gifts were given to the other believers.

"they will speak with new tongues₁"

Christ merely meant tongues that they had not spoken and were different from those with which they were normally familiar. See Acts 2, Acts 19:6.

Mark 16:18

"they will pick up serpents, and if they drink any deadly thing, it shall not hurt them;" see Acts 28:5, Luke 10:19.

‘It is understandable that in an age dominated by a wonder-working paganism, these vivid and incontestable tokens of true divine power would be necessary as a decisive witness against the vested interests of well-organized cults of magic. Today the same signs would probably be more of a hindrance than a help to the well-balanced preaching of God’s saving grace in Christ. Indeed it is not altogether untrue to say that even the mention of signs here is read by some modern believers with misgivings: casting out devils, speaking with tongues, handling deadly snakes, drinking poison, healing the sick by the laying on of hands. Why should these powers be imparted to the early church and then so soon disappear, leaving later generations to apologize lamely for current ineffective witness and also leaving the door wide open for sensational charlatans with loud-mouthed claims to be the heirs of apostolic powers?

The withdrawal of the gifts of the Spirit is a thing to be profoundly thankful for. For, in the first place, this lapse of open Spirit blessing would never have happened had it not been in the best interests of the believers. The Lord has certainly done what is best for the well-being of his people. But, further, let it not be forgotten that the key virtue in Christian life is faith. What very limited scope there would be for faith today if these signs were openly available for the confutation of unbelief! "Blessed are they that have not seen (either empty tomb or Holy Spirit powers), and yet have believed." ’₁

Some ecstatic holiness churches in Kentucky, U.S.A. have taken up snake handling as evidence of "faith". Here a poisonous rattlesnake is handled at a meeting. The lay preacher holding the snake subsequently died from snakebite at a later meeting. (Religious Sects: Wilson)