I have come to find out by reading the Psalms and other portions of God's word (the Bible) that what we will do is more important that what we should do--for this wise counsel applies to every situation of life. For instance, knowing we should wash the car because we cannot see out of the windows is not as important as washing the car. The Bible is packed with revelations and affirmations of God's will for our lives that is as relevant for household chores, business decisions and personal relationships--really everything.
When David was on the run from king Saul who sought his life, there were many decisions he needed to make concerning himself, his family and men. What David said "I will" to is revealed to be God's will for us in every season of life, and when we do this we do well. Psalm 18:1-3 says, "I will love
You, O LORD, my strength. 2 The LORD is my rock and my fortress and my
deliverer; my God, my strength, in whom I will trust; my shield and the horn of my salvation, my
stronghold. 3 I will call upon the LORD, who is worthy to be
praised; so shall I be saved from my enemies." While loving God did nothing to stop king Saul murderous rampage or save David's life, that is what David decided he would do by faith in God who is worthy to be trusted and praised.
David did not say, "I should love the LORD" because that suggests he had stopped short of demonstrating love to God. David said, "I will love You, O LORD" and "in God I will trust" because God was his rock, fortress, deliverer, strength, shield, salvation and stronghold. He said, "I will call upon the LORD." David did not say "I will try" to do these things, but by faith in God to do and continue doing these things regardless of the circumstances of his life. Instead of being stricken with the self-inflicted guilt and regret of "should do," Christians can have the "I will" outlook and God-honouring lifestyle of following God's will every day.