FOR THOSE WHO ARGUE THAT YOU DON'T HAVE TO BE BAPTIZED TO BE SAVED, YOU GET BAPTIZED BY THE HOLY SPIRIT THE MOMENT YOU BELIEVE.
"He that believeth and is baptized shall be saved; but he that disbelieveth shall be condemned."
There is one body, and one Spirit, even as also ye were called in one hope of your calling; one Lord, one faith, one baptism, one God and Father of all, who is over all, and through all, and in all.
The one baptism is not by the Holy Spirit. Instead, when we are baptized, we receive the gift of the Holy Spirit.
And Peter said unto them, "Repent ye, and be baptized every one of you in the name of Jesus Christ unto the remission of your sins; and ye shall receive the gift of the Holy Spirit."
1 PETER 3:18-22
Because Christ also suffered for sins once, the righteous for the unrighteous, that he might bring us to God; being put to death in the flesh, but made alive in the spirit; in which also he went and preached unto the spirits in prison, that aforetime were disobedient, when the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls, were saved through water: which also after a true likeness doth now save you, even baptism, not the putting away of the filth of the flesh, but the interrogation of a good conscience toward God, through the resurrection of Jesus Christ; who is one the right hand of God, having gone into heaven; angels and authorities and powers being made subject unto him.
Baptism requiring water is repeated throughout the New Testament.
And as they went on the way, they came unto a certain water; and the eunuch saith, "Behold, here is water; what doth hinder me to be baptized?" And Philip said, "If thou believest with all thy heart, thou mayest." And he answered and said, "I believe that Jesus Christ is the Son of God."
While Peter yet spake these words, the Holy Spirit fell on all them that heard the word. And they of the circumcision that believed were amazed, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Spirit. For they heard them speak with tongues, and magnify God. Then answered Peter, "Can any man forbid the water, that these should not be baptized, who have received the Holy Spirit as well as we?"
Or are ye ignorant that all we who were baptized into Christ Jesus were baptized into his death? We were buried therefore with him through baptism unto death: that like as Christ was raised from the dead through the glory of the Father, so we also might walk in newness of life. For if we have become united with him in the likeness of his death, we shall be also in the likeness of his resurrection; knowing this, that our old man was crucified with him, that the body of sin might be done away, that so we should no longer be in bondage to sin; for he that hath died is justified from sin. But if we died with Christ, we believe that we shall also live with him; knowing that Christ being raised from the dead dieth no more; death no more hath dominion over him. For the death that he died, he died unto sin once: but the life that he liveth, he liveth unto God. Even so reckon ye also yourselves to be dead unto sin, but alive unto God in Christ Jesus.
But he gives more grace; therefore it says, "God opposes the proud, but gives grace to the humble."
If we receive God's grace, and thereby salvation, by believing and nothing else is necessary, then this passage would mean that only the humble should bother to believe because others would not receive His grace. All who believe and are baptized receive God's grace; we need to work to become humble and stay humble.
Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Believing and calling Christ your Lord are not enough, we must do what Christ said - including getting baptized - and we must do it with a good heart and the right attitude. Getting baptized after you are "saved" just as an sign to others is not doing the will of God.