Because I do not understand why you keep equivocating baptism with the elect only.
Clearly, the difference is in how we view the meaning of baptism. We understand baptism as the sign given to a new believer that identifies them with Christ's death and resurrection. It symbolizes our dying to self and living a new life in Christ. This is why we always come to this point in these discussions! <img src="/forum/images/graemlins/Banghead.gif" alt="" /> We do not see baptism replacing the sign of circumcision as the paedobaptists do. There are some parallels, but there are differences as well. We don't deny that both baptism and circumcision are both signs of the covenant, an identification given by God to the church and to Israel .
Romans 6:1What shall we say then? Are we to continue in sin that grace may abound? 2 By no means! How can we who died to sin still live in it? 3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
5 For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. 6 We know that our old self  was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. 7 For one who has died has been set free  from sin. 8 Now if we have died with Christ, we believe that we will also live with him. 9 We know that Christ being raised from the dead will never die again; death no longer has dominion over him. 10 For the death he died he died to sin, once for all, but the life he lives he lives to God. 11 So you also must consider yourselves dead to sin and alive to God in Christ Jesus.
12 Let not sin therefore reign in your mortal bodies, to make you obey their passions. 13 Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness. 14 For sin will have no dominion over you, since you are not under law but under grace.
Colossians 2: 9 For in him the whole fullness of deity dwells bodily, 10 and you have been filled in him, who is the head of all rule and authority. 11 In him also you were circumcised with a circumcision made without hands, by putting off the body of the flesh, by the circumcision of Christ, 12 having been buried with him in baptism, in which you were also raised with him through faith in the powerful working of God, who raised him from the dead. 13 And you, who were dead in your trespasses and the uncircumcision of your flesh, God made alive together with him, having forgiven us all our trespasses, 14 by canceling the record of debt that stood against us with its legal demands. This he set aside, nailing it to the cross. 15 He disarmed the rulers and authorities  and put them to open shame, by triumphing over them in him. 
We, just like you, draw lines between believers and unbelievers. You examine candidates before admitting them to the Lord's Table as communicant members. Unlike you, we draw that line at baptism. John Dagg on Church Membership "The churches are not infallible judges, being unable to search the heart but they owe it to the candidate [for membership] himself, to exercise the best judgment of which they are capable. To receive any one on a mere profession of words, without any effort to ascertain whether he understands and feels what he professes, is unfaithfulness to his interests, and the interests of religion."