One cannot be saved by the Spirit only, nor by baptism only.
One needs both.
You have heard of the baptism of the Holy Spirit, right? The one Jesus baptizes us at our salvation? The One the Father sends as promised at our salvation? That is the baptism spoken of in Mark 16:16 for why by not believing in Him is how they are not saved.
John 1:32 And John bare record, saying, I saw the Spirit descending from heaven like a dove, and it abode upon him. 33 And I knew him not: but he that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on him, the same is he which baptizeth with the Holy Ghost. 34 And I saw, and bare record that this is the Son of God.
Matthew 3:15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness. Then he suffered him. 16 And Jesus, when he was baptized, went up straightway out of the water: and, lo, the heavens were opened unto him, and he saw the Spirit of God descending like a dove, and lighting upon him: 17 And lo a voice from heaven, saying, This is my beloved Son, in whom I am well pleased.
John 14:1Let not your heart be troubled: ye believe in God, believe also in me.....6 Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.....16 And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever; 17 Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.....25 These things have I spoken unto you, being yet present with you. 26 But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.