By Example

It was by faith that Abel brought a more acceptable offering to God than Cain did. Abel’s offering gave evidence that he was a righteous man, and God showed his approval of his gifts. Although Abel is long dead, he still speaks to us by his example of faith.
Hebrews 11:4 NLT

Abel was a righteous man. God approved of Abel's offerings but did not approve of Cain's. So out of anger born of jealousy, Cain murdered Abel... and yet it is Abel's example of faith that still speaks to us.

What does it say? God was very specific about what offerings were acceptable. Abel listened and obeyed. He brought to God what God had required. Cain brought what he wanted, thereby placing himself above God. It's not just our actions that matter to God, it's the attitude of our hearts, as well. 

Prayer:

Father,

           Please forgive us for bad attitudes. Change our hearts, O God! Let all that we say and do be pleasing to You. Let the examples of our faith speak Life, Truth and Light to those coming after us. In Jesus' Name we pray. Amen