Number TWO is the number for WITNESS
See Old Testament: Deut' 19 vs 15 (One witness is not enough to convict anyone accused of any crime or offense they may have committed. A matter must be established by the testimony of two or three witnesses.)
New Testament: Matthew 18 vs 16 (Words of Jesus) (But if they will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.')
In what circumstances of life do we need a witness?
Obviously to witness an event, in law, to sort out who said what-to whom etc
According to the Bible we must have a Witness in Conversion and in Conviction;
1) IN CONVERSION: Romans 8 vs 16 says 'The Spirit Himself Testifies with our Spirit that we are the Children Of God'
So the two witnesses in Conversion are The Holy Spirit and Our Spirit
2) IN CONVICTION: God witnesses to us to Convince us of:
a) His Presence: see Mat 18 vs 20 (Notice the two witnesses) (For where two or three gather in my name, there am I with them.)
b) Answered Prayer: see Mat 18 vs 19 (Notice the two witnesses) (Again, truly I tell you that if two of you on earth agree about anything they ask for, it will be done for them by my Father in heaven)
c) Belief in the resurrection: Two witnesses constantly occur in gospels
2 angels at the tomb-Luke 24 vs 2 to 6 (2 And they found the stone rolled away from the sepulcher. 3 And they entered in, and found not the body of the Lord Jesus.4 And it came to pass, as they were much perplexed thereabout, behold, two men stood by them in shining garments:5 And as they were afraid, and bowed down their faces to the earth, they said unto them, Why seek ye the living among the dead?6 He is not here, but is risen: remember how he spake unto you when he was yet in Galilee)
2 disciple on the road to Emmaus Luke 24:32 (They asked each other, “Were not our hearts burning within us while he talked with us on the road and opened the Scriptures to us?”)
At least 2 eye witnesses of the resurrection 1 Cor'15 vs 3 to 8 (For what I received I passed on to you as of first importance[a]: that Christ died for our sins according to the Scriptures, 4 that he was buried,that he was raised on the third day according to the Scriptures, 5 and that he appeared to Cephas, and then to the Twelve. 6 After that, he appeared to more than five hundred of the brothers and sisters at the same time, most of whom are still living, though some have fallen asleep. 7 Then he appeared to James, then to all the apostles, 8 and last of all he appeared to me also, as to one abnormally born.)