Giving is just one aspect of the greater subject of stewardship, which encompasses everything that God has given believers. These range from material goods to spiritual gifts, knowledge and abilities. The giving aspect of stewardship deals specifically with monetary issues, i.e. that which God gives the believer and the portion returned to Him by means of supporting the Lord's work.
James 1:17 tells us that "Every good gift and every perfect gifts is from above, and comes down from the Father of light, with whom there is no variation or shadow of turning."
1. God owns all things (Psalm 24:1 and Haggai 2:8)
2. God is the Creator, Make and Giver of all things.
3. By giving, the believer is returning a portion of that which belongs to God, anyway. Luke 6:38 tells us our return on giving.