The reasons for the WORK of the Believer:

Let your light so shine before men, that they may see your good WORKS and glorify your Father which is in heaven. Matthew 5:16

Therefore, my beloved brethren, be ye steadfast, unmovable, always abounding in the WORK of the Lord, forasmuch as ye know that your labor is not in vain in the Lord. 1st Corinthians 15:58

For we are His WORKMENSHIP created in Christ Jesus unto good WORKS, which God has before ordained that we should walk in them. Ephesians 2:10

For it is God which WORKETH in you both to will and to do of His good pleasure. Philippians 2:13

And, behold, I come quickly; and my reward is with me, to give every man according as his WORK shall be. Revelation 22:12