The Meaning of Baptism in Water  
This writing does not go into the pros and cons of adult baptism - there are plenty of those out there for those who don't understand the concept. 
This goes into the spiritual nature of your act of obedience and is an addendum to the preceding article "Our Old Man." To understand this teaching you will need to understand the other first. 
As we saw before, first comes faith, then grace: 
Therefore being justified by faith, we have peace with God through our Lord Jesus Christ: By whom also we have access by faith into this grace wherein we stand, and rejoice in hope of the glory of God. 
(Romans 5:1-2)
It's when we understand the next passage that the hidden treasure starts being revealed to us: 
8 But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us. 9 Much more then, being now justified by his blood, we shall be saved from wrath through him. 10 For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. 11 And not only so, but we also joy in God through our Lord Jesus Christ, by whom we have now received the atonement. 
(Romans 5:)
From studying "Our Old Man" we now understand verse eight. 
From verses nine and ten we understand that through the Covenant of Blood of our Covenant Representative, who at the same time was the Sacrificial Lamb, we are once more reconciled (redeemed) to God. Once we are deemed afresh, God notices us again; and when we have faith that Jesus rose from the dead by the power of God, we shall be saved. 
Please notice the word tenses here. 
  • Christ died for us in the past. 
  • When we accept the Covenant of His Blood we are reconciled (present tense). 
  • When we accept the Truth of His resurrection we shall be saved (future tense). 
With this understanding behind us, let's once more go to Romans chapter six: 
Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. For he that is dead is freed from sin. Now if we be dead with Christ, we believe that we shall also live with him: Knowing that Christ being raised from the dead dieth no more; death hath no more dominion over him. For in that he died, he died unto sin once: but in that he liveth, he liveth unto God. Likewise reckon ye also yourselves to be dead indeed unto sin, but alive unto God through Jesus Christ our Lord. 
(Romans 6:3-11)
Please study the tenses again.
These passages of Scripture therefore show us that baptism is far more than getting wet all over. It's an act of obedience that has spiritual power. 
Remember what the Bible teaches us about obedience: 
And we are his witnesses of these things; and so is also the Holy Ghost, whom God hath given to them that obey him. 
(Acts 5:32)
In verse 5 of Romans chapter six we notice a very significant teaching, namely that like the dead seed which is planted, when watered by the Holy Spirit the new plant which comes up shall be like the resurrected Christ. 
For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection: 
In this process of repentance and obedience we shall receive the Holy Spirit living inside of us. 
This, however, is different from being baptised in the Holy Spirit. A happening that empowers each of us to use our talents for the glory of God. 
By your fruits are you known.