How do you explain Mark 16:17-18 concerning signs?
We settle in our minds first of all, that since the Lord said that these signs would follow them that believe (have believed), then they actually took place. Notice that these were not signs that followed those who preached, but those who believed. The Lord says that these signs “will follow” without stipulating any special condition apart from believing. Signs were given in the early days of the Spirit’s working on earth after Pentecost, and these were needed for that period. They served to prove to the Jews that this was a real, divine work, either to counter the opposition of some, or to confirm those who were looking for the Messiah and a movement of the Holy Spirit. These signs are similar to the sign gifts that are listed by Paul (1Cor 12) and what he mentions later (2Cor 12:12), particular endowments by the Holy Spirit that were needed for that time, but were not intended to continue.
It is easy to read into the passage what is not there. The Lord didn’t say that they were to be expressed in all that have believed, in all places, and at all times. The fact of their occurrence at certain times by certain individuals was intended to prove the reality of this salvation by grace alone through faith in Christ. If not, then one would have to conclude that we are not saved today if we don’t demonstrate these same signs! In Acts we read accounts of four out of the five signs. Paul cast the demon out of the damsel in Acts 16:18, and the same was accomplished in Acts 5:16 and 8:7 by others. The disciples spoke with new tongues in Acts 2:4-11 and 10:46. Paul was unaffected by the bite of the poisonous viper in Acts 28:3-6, and while we have no record of them drinking deadly things, we can be sure that it took place. We see them laying hands on the sick and healing them on numerous occasions in Acts, such as in 3:6-8, 5:15-16, 9:34, 40-42; 28:8-9. So the Lord’s words were fulfilled (as they always are), and the power of God attested to the nature of the work that was taking place among them.