Will of God

Matthew 7:21 KJV
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.

What is the will of the Father talked about in Matthew 7:21?

John 6:28-40 KJV
Then said they unto him, What shall we do, that we might work the works of God? 
[29] Jesus answered and said unto them, This is the work of God, that ye believe on him whom he hath sent. 
[30] They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work? 
[31] Our fathers did eat manna in the desert; as it is written, He gave them bread from heaven to eat. 
[32] Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but my Father giveth you the true bread from heaven. 
[33] For the bread of God is he which cometh down from heaven, and giveth life unto the world. 
[34] Then said they unto him, Lord, evermore give us this bread. 
[35] And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and he that believeth on me shall never thirst. 
[36] But I said unto you, That ye also have seen me, and believe not. 
[37] All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out. 
[38] For I came down from heaven, not to do mine own will, but the will of him that sent me. 
[39] And this is the Father's will which hath sent me, that of all which he hath given me I should lose nothing, but should raise it up again at the last day. 
[40] And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.

1 John 2:17 KJV
And the world passeth away, and the lust thereof: but he that doeth the will of God abideth for ever.

How can you abide forever by doing the will of God?

John 3:16 KJV
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.

By believing on his Son (John 3:16).

The will of God regarding eternal salvation is that you believe on his Son.

Mark 3:35 KJV
For whosoever shall do the will of God, the same is my brother, and my sister, and mother.

You become a brother or sister of Christ when you get saved which you become when you believe on Jesus Christ.

1 Corinthians 15:3-4 KJV
For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; [4] And that he was buried, and that he rose again the third day according to the scriptures:

1 Thessalonians 4:3 KJV
For this is the will of God, even your sanctification, that ye should abstain from fornication:

That we abstain from fornication is the will of God regarding sanctification, but it is not an eternal salvation issue.

Eternal salvation happens in an instant. It happens when you believe on the Lord Jesus Christ. Then you cannot lose your eternal salvation.

Ephesians 1:12-13 KJV
That we should be to the praise of his glory, who first trusted in Christ. 
[13] In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,

Galatians 1:4 KJV
Who gave himself for our sins, that he might deliver us from this present evil world, according to the will of God and our Father:

See in Gal 1:4 that we are delivered from this present evil world by believing on his Son. This happens in an instant. This is the will of God.

Hebrews 10:36 KJV
For ye have need of patience, that, after ye have done the will of God, ye might receive the promise.

When you have believed on the Lord Jesus Christ you receive the promise. The will of God in Heb 10:36 is that you believe on his Son.