Action is a physical act of manipulating something within time and space. Taking a step forward is a manipulation of muscle and bone to move the leg and this represents an action. Desire however is an idea in the mind and is the act of manipulating the spirit. Desire is not a manipulation of time and space however desire can and often does lead to action. Some actions are reflexive but many actions are deliberate and are the direct result of desire that has built up over time.
If I desire to steal but never act upon that desire is it a sin before God? If I desire to steal but never have opportunity because of some constraint (like fear of getting caught) is it a sin before God?
Moses arguably the greatest leader and judge of Israel was told by God that he would not be allowed to lead Israel into the promised land because of one time where he did not “uphold [God] as holy”
10 Then Moses and Aaron gathered the assembly together before the rock, and he said to them, “Hear now, you rebels: shall we bring water for you out of this rock?” 11 And Moses lifted up his hand and struck the rock with his staff twice, and water came out abundantly, and the congregation drank, and their livestock. 12 And the Lord said to Moses and Aaron, “Because you did not believe in me, to uphold me as holy in the eyes of the people of Israel, therefore you shall not bring this assembly into the land that I have given them.” Numbers 20:10-12 ESV
Now Moses was told by God to bring water from a rock to allow the people to drink while in the dessert and Moses did that. God through Moses brought the water out of the rock, but Moses failed to represent God as holy in the situation. The standards God has set for our desires and our actions is beyond what any person can follow. Moses who has seen the physical holy representation of God whose very hand carved into stone the 10 commandments is being held to an even higher standard than the average person. Moses failed to keep God holy before the people and Moses knew better. His actions in time and space brought forth water out of a rock but his desires, his anger with the people for being such awful whiny complainers had made him angry. Maybe his anger with the people or something as priest like he failed to give thanks to God resulted in God calling out his desire as a sin.
Paul talks about desire to the early church and keeping Moses in mind read what Paul states about leadership and where desire should be focused.
3 For our appeal does not spring from error or impurity or any attempt to deceive, 4 but just as we have been approved by God to be entrusted with the gospel, so we speak, not to please man, but to please God who tests our hearts. 1 Thessalonians 2:3-4 ESV
Many people I talk with about God will state something along the lines of “God will see I am a good person and will see that my good outweighs my bad. What more can I do?” This is the wrong perspective because it follows the worlds obsession with the physical actions. Notice the focus on actions of good and bad results. “I am not as bad as that person my actions are much better.”
Just like when I move a foot to take a step forward I must first desire in my heart and spirit to move that foot forward. How many times have I thought I should take a step forward and failed to do so? I will be accountable to God for those desires that were never even acted on.
Do not think God will only see our actions and our actions are those of a good person. Know that God will judge our heart and our desires. He knows the hate I have had for others even if I did not act out the violence in my heart. He knows that I have desired the money of my neighbor even though I never robbed him. He knows that I have lusted for the physical comforts of this world to satisfy my own selfish desires to the detriment of brothers and sisters. What a wretched heart that lives in me. Forgive me father for my sins of both action and desire. Thank you for Jesus who has taken those sins from me that I may humbly sit before you as a child restored to his father.