"And here men that die receive tithes; but there he receiveth them, of whom it is witnessed that he liveth." (Hebrews 7: 8)
When we tithe, we are testifying that Jesus is alive and serving us.
"And he says in another place, "You are a priest forever, in the order of Melchizedek." (Hebrews 5: 6)
"31What shall we then say to these things? If God be for us, who can be against us? 32He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things? 33Who shall lay any thing to the charge of God's elect? It is God that justifieth. 34Who is he that condemneth? It is Christ that died, yea rather, that is risen again, who is even at the right hand of God, who also maketh intercession for us." (Romans 8: 31-34)
In the passage above, we find Paul writing about Jesus our living Savior, who is ministering on our behalf actively, right now.
We do not tithe, therefore, to move God to do something for us, but rather as a testimony that He is alive, living in us, through us, and for us.
"3Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ: 4According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: 5Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, 6To the praise of the glory of his grace, wherein he hath made us accepted in the beloved."" (Ephesians 1: 3-6)
"21Therefore let no man glory in men. For all things are yours; 22Whether Paul, or Apollos, or Cephas, or the world, or life, or death, or things present, or things to come; all are yours; 23And ye are Christ's; and Christ is God's." (1 Corinthians 3: 21-23)
Let us never forget that anything that we have, all is the gift of God:
"8For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: 9Not of works, lest any man should boast. 10For we are his workmanship, created in Christ Jesus unto good works, which God hath before ordained that we should walk in them." (Ephesians 2: 8-10)
We tithe to reap what God has already sown, too:
"7Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap. 8For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting. " (Galatians 6: 7-8)
In the previous chapter, Paul wrote about the fruit of the Spirit (Galatians 5: 22-23), all of which comes from His Spirit, not from our striving.
Anything we release back to God, is a response to all that He has given us.
And the first, the greatest thing which God gave, His Son, provided us with His life:
"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." (John 3: 16)
"When Christ, who is our life, shall appear, then shall ye also appear with him in glory." (Colossians 3: 4)