Scripture

Luke 8:21  But He answered and said to them, "My mother and My brothers are these who hear the word of God and do it."

Observation

(A lot of words are in past tense, the definitions are not always changed to past tense, it is understood we will make that change ourselves as we study.)

But

• *on the contrary
• except; save
• unless; if not; except that

He  - Jesus

answered

• *spoken or written reply or response to a question, request, letter, etc.
• a correct response to a question asked to test one's knowledge
• an equivalent or approximation
• an action serving as a reply or response
• solution to a problem
• reply to a charge or accusation

and

• along or together with
• added to; plus
• *then
• then again; repeatedly
• also (implying continuation)

said - (past tense of say)

• utter; pronounce; speak
• express in words

to

• express motion/direction toward a point
• express limit of movement
• express aim, purpose, or intention

them,  - the people who told Him His mom and brothers were outside

"My  - Jesus

mother

• female parent

and - also (see above)

My  - Jesus

brothers

• male siblings
• male numbered among the same kinship group, nationality, race, profession, etc., as another; an association; a fellow member, fellow countryman, fellow man 
• a man who devotes himself to the duties of a religious order without taking holy orders, or while preparing for holy orders.

are  - present plural of "be", exist

these - the people

who  - the people with Him

hear

• perceive by ear
• learn by ear or being told
• *to listen to; give or pay attention to
• be among the audience

the - used before a noun to stress a particularizing effect

word

• a unit of language consisting of one or more spoken sounds or written representations that functions as a principal carrier of meaning.
• speech or talk to express

of

• used to indicate distance or direction from
• *used to indicate derivation, origin, or source 
• used to indicate cause, motive, occasion, or reason

God

• Supreme Being, Creator, Ruler of the universe 
• Father in the Trinity
•  lower case (god) image of the Creator
• lower case (god) any deified person or object

 and

• along or together with
• added to; plus
• then
• then again; repeatedly
• *also

do

• to perform
• to execute
• to accomplish; finish; complete
• to put forth; exert

 it."  - the word of God

They spoke to Jesus.

Jesus answered.

He did not ignore their statement and keep teaching.  He acknowledged them. 

They were probably nervous and uncomfortable with Him teaching and His family outside...I would be nervous and unable to pay attention to His teaching if I were there, worrying about the circumstance.  I would be looking back and forth between them on the outside and Him teaching and not concentrating on His teachings. 

Mother and brothers.  I'm guessing He said this because those were the members of the family that were mentioned, but that sisters would have been included in His answer had they been mentioned in by the "some" who spoke to Him.

He is saying those who hear - actively pay attention to God's Word and also do what He says (live what He says), are His family.

Application

We are members of His family if we exert/do/live what He says.

We will only know what He says if we actively listen/read His word.

Reading passage sections through (a parable, an event, a particular teaching, etc.), before taking a verse word-by-word like this, is important.  There have been verses that I have taken one word at a time without reading the passage, only to realize, after much digging, I was digging in the wrong direction.  Oops. 

Prayer

Father God, thank You for Your Word.  Jesus, thank You for answering when I come to You.  Thank You for not telling me I'm an interruption.  Father, thank You for adopting me into Your family and making me Your daughter, sister of Jesus.  Wow.  That sounds weird when I say that.  Thank You also for following my thoughts when they drift and for knowing what I mean, even I sometimes lose track of what I was coming to You about.  Thank You for giving me family members to come along side me when my biological family cannot be with me.  Thank You for Your faithfulness.  Help me to live out Your Word. I pray in Your name, Jesus.  Amen.