Of course it is absolutely necessary to be baptized by full immersion
in water.
Jesus did it as a demonstration to fulfill all righteousness.
Jesus commanded it more than once in the gospels.
To become a Christian Peter tells us in response to the question:
Men and brethren, what shall we do?
38 Then Peter said unto them, Repent, and be baptized every one of you in the
name of Jesus Christ for the remission of sins, and ye shall receive the gift of
the Holy Ghost.
39 For the promise is unto you, and to your children, and to all that are afar off,
even as many as the Lord our God shall call.
40 And with many other words did he testify and exhort, saying, Save yourselves
from this untoward generation.
41 Then they that gladly received his word were baptized: and the same day there
were added unto them about three thousand souls.
Acts 2:
Peter again writes of baptism as an expression of a good conscience towards
God unto obedience - that is not arguing with the commandments of God.
Romans chapter 6 is all about water baptism and the symbolism and purpose of such.
Death and burial to the old person, rising up to embrace resurrection in Christ Jesus;
hence also the need for Holy Spirit baptism.
Acts is full of examples showing that Christians were baptized in water and then
also sought for the gift of the Holy Spirit.
Verses pertaining to baptism are scattered all throughout the epistles because it
was expected that ALL converts were baptized by full immersion and baptized
in the Holy Spirit.
Obedience is what discipleship is all about.
And now why tarriest thou? arise, and be baptized, and wash away thy sins,
calling on the name of the Lord.
Acts 22:16