I'll deal with one issue at a time. Since you're glad we're discussing Acts15:7-9, we should be in agreement to deal with whatever we actually find there and hopefully to do so with more depth than you're putting forth.
Previously I had to do the work to dispel the notion you presented regarding what Jewish references you identified said about baptism.
Now we'll work on your above claim about witness in Acts15:8:
There are 25 instances of 'witness' in Acts. If you'd like to go through them one at a time or in bulk including each one, let me know. Here are a few findings:
God witnesses to people in Acts:
Acts5:32 the Holy Spirit is a co-witness with the Apostles to the Sanhedrin about Jesus
Acts13:22 God witnesses to Israel about King David's heart
Acts14:3 The Lord witnesses to Iconium about the truth of the Word/Message of Grace
Acts15:8 God the knower of hearts witnesses to Peter and the Jews about the Gentiles’ receipt of the Gospel
'Witness' + [Dative Construction] in Acts:
- Acts10:43 All the Prophets witness [] Jesus Christ
- The Prophets don’t witness to Jesus – The Prophets witness to men about Jesus
- Acts13:22 King David [] whom God witnessed
- God didn’t witness to David – God witnessed to Israel about David
- Acts14:3 The Lord witnessed [] the Word/Message of His Grace
- The Lord didn’t witness to His Word – The Lord witnessed to people about His Word
- Acts15:8 God the knower of hearts witnessed [] the Gentiles
- God didn’t witness to the Gentiles – God witnessed to Peter and the Jews about the Gentiles
- Acts22:5 The high priest witnessed [] Paul
- The high priest didn’t witness to Paul – The high priest witnessed to men about Paul
In all 25 instances of 'witness' in Acts, the word describes the legal deposition of evidence to establish a fact. In Acts15:8, God isn't 'witnessing' to the Gentiles to save them; He is 'witnessing' to the Jewish church to prove He is giving repentance to the Gentiles (Acts11:18). This witness was also God’s authorization for Peter to proceed with the commanded water baptism (Acts 10:48). To ignore God's witness and refuse the water baptism, as Peter concluded, would be 'withstanding/preventing/forbidding God' (Acts 11:17).
IMO the KJV and NKJ do the better work in translating Acts15:8:
KJV Acts 15:8 And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
NKJ Acts 15:8 "So God, who knows the heart, acknowledged them by giving them the Holy Spirit, just as He did to us,
When dealing with the Greek language, the grammatical issue we're dealing with here is the Dative Case. Here are the choices Daniel Wallace provides in Greek Beyond the Basics for interpreting the Dative. If you're going to tell us what Acts15:8 is saying in regard to God's witness and what He is doing in witnessing there, you're going to have to explain your reasoning from Greek grammar (and from the way Luke writes and Peter speaks about 'witness' in Acts):
The Dative Case
Overview of Dative Uses
Pure Dative Uses
140
1. Dative Indirect Object
140
2. Dative of Interest (including Advantage [
commodi] and Disadvantage [
incommodi])
142
3. Dative of Reference/Respect
144
5. Dative of Destination
147
6. Dative of Recipient
148
7. Dative of Possession
149
8. Dative of Thing Possessed
151
10. Dative in Simple Apposition
152
Local Dative Uses
153
3. Dative of Time (when)
155
Instrumental Dative Uses
158
1. Dative of Association
159
2. Dative of Manner (or Adverbial Dative)
161
3. Dative of Means/Instrument
162
5. Dative of Measure/Degree of Difference
166
8. Dative of Material
169
9. Dative of Content
170
The Uses of the Dative After Certain Words
171
1. Dative Direct Object
171
2. Dative After Certain Nouns
173
3. Dative After Certain Adjectives
174
4. Dative After Certain Prepositions
175
Let me know if I can help.