Oh my good old friend JLB. Certainly, I'd be glad to share my theology on the second Baptism.
I guess most every Christian knows that at Salvation, a believer is baptized by the Holy Spirit into the family of God. So I doubt that you want me to elaborate. Lets look at Acts 1 verse 5.
Acts 1:5 "For John truly baptized with water; but ye shall be baptized with the Holy Ghost not many days hence." We have here the working out of a promise of God, as it says right before this verse. This verse mentions John's baptism, now we are talking about a second Baptism. The word "with" which is mentioned twice in this verse should be Gk. ἐν which is "in" Strongs, G1722 This change is so important to me for a correct understanding of this verse. SO, the verse should read, For John truly baptized IN water; but you shall be baptized IN the Holy Ghost not many days hence."
Now the verse is making a little more sense. John immersed people IN water. That is a clue that baptism other than immersion is not biblical, because it's IN water. Now we come to the Holy Ghost, or Spirit. We are baptized IN the Holy Spirit. Wow, what does that mean? There is a job to do now that Jesus has ascended to His heavenly throne. There is work to be done to reach the lost with the Gospel of Jesus Christ. That job is to be a witness to them, not in human power, but with God's power.
Now lets look at what Jesus said about the Holy Spirit of Whom we are going to enter as we become baptized into Him.
John 16:4 But these things have I told you, that when the time shall come, ye may remember that I told you of them. And these things I said not unto you at the beginning, because I was with you.
16:5 But now I go my way to him that sent me; and none of you asketh me, Whither goest thou?
16:6 But because I have said these things unto you, sorrow hath filled your heart.
16:7 Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you.
16:8 And when he is come, he will reprove the world of sin, and of righteousness, and of judgment:
16:9 Of sin, because they believe not on me;
16:10 Of righteousness, because I go to my Father, and ye see me no more;
16:11 Of judgment, because the prince of this world is judged.
16:12 I have yet many things to say unto you, but ye cannot bear them now.
16:13 Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, that shall he speak: and he will shew you things to come.
16:14 He shall glorify me: for he shall receive of mine, and shall shew it unto you.
16:15 All things that the Father hath are mine: therefore said I, that he shall take of mine, and shall shew it unto you.
Humanly speaking, we can't convict anyone of their sin, or explain the righteousness of Jesus, but the Holy Spirit can! The Holy Spirit needs a human to come into Him for this work. Actually, we are being placed IN His power. To be baptized in the Holy Spirit is to jointly be with Him and His power and work to save the lost, it becomes you and the Holy Spirit going about as a witness to the world, or your sphere of witness for the Glory of God.
Speaking in tongues is just one of the gifts of the Holy Spirit. Chapter twelve of 1 Corinthians lists all the gifts. Tongues was the first sign at Pentecost to alert all those people that something supernatural was happening. Since then, the Church of Jesus Christ expanded, and was organized. Once these local churches were established, the need for all the gifts came into being. Tongues is not the only sign that a person is in the Holy Spirit, love may be the best sign.
I hope this answers your question JLB, I'd be happy to explain any part of my theology. Be Blessed my friend.