Faith is necessary to please God.
The Bible asserts that faith is necessary to please GOD:
6 And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
(Hebrews 11:6 NIV)
We have previously established what faith means: action resulting from one's belief in things they cannot see.
1 Now faith is confidence in what we hope for and assurance about what we do not see.
(Hebrews 11:1 NIV)
It is critical to understand that biblical faith is the combination of belief (trust) and action that results from that belief.
Regarding Abraham, the father of the faithful, there are two interesting New Testament passages that affirm this combination of trust and action. The apostle Paul pointed out that Abraham's justification (his declaration of being righteous) was not by works (the actions that Abraham performed), but by faith:
1 What then shall we say that Abraham, our forefather according to the flesh, discovered in this matter? 2 If, in fact, Abraham was justified by works, he had something to boast about—but not before God. 3 What does Scripture say? “Abraham believed God, and it was credited to him as righteousness.”
(Romans 4:1-3 NIV)
While Abraham was justified by his belief in GOD (and GOD's promises), it was Abraham's obedience that confirmed Abraham's faith. James, the brother of Jesus, wrote:
14 What good is it, my brothers and sisters, if someone claims to have faith but has no deeds? Can such faith save them? 15 Suppose a brother or a sister is without clothes and daily food. 16 If one of you says to them, “Go in peace; keep warm and well fed,” but does nothing about their physical needs, what good is it? 17 In the same way, faith by itself, if it is not accompanied by action, is dead.
18 But someone will say, “You have faith; I have deeds.”
Show me your faith without deeds, and I will show you my faith by my deeds. 19 You believe that there is one God. Good! Even the demons believe that—and shudder.
20 You foolish person, do you want evidence that faith without deeds is useless? 21 Was not our father Abraham considered righteous for what he did when he offered his son Isaac on the altar? 22 You see that his faith and his actions were working together, and his faith was made complete by what he did. 23 And the scripture was fulfilled that says, “Abraham believed God, and it was credited to him as righteousness,” and he was called God’s friend. 24 You see that a person is considered righteous by what they do and not by faith alone.
25 In the same way, was not even Rahab the prostitute considered righteous for what she did when she gave lodging to the spies and sent them off in a different direction? 26 As the body without the spirit is dead, so faith without deeds is dead.
(James 2:14-26 NIV)
But what makes faith so important—so necessary—in GOD's mind?
For one, we must remember that GOD is invisible. GOD is Spirit. GOD gave humans five senses: sight, smell, touch, taste, hearing. None of these senses can (at least, not fully) experience GOD. Even when GOD spoke directly to people, such as Adam and Noah, faith (trust + obedience) was still necessary. And even more so for those of us with whom GOD does not directly interact. Jesus acknowledged this with the doubting apostle Thomas:
29 Then Jesus told him, “Because you have seen me, you have believed; blessed are those who have not seen and yet have believed.”
(John 20:29 NIV)
Secondly, mortal flesh is weak. Human thinking, speech, and actions are driven by reliance upon our fleshly senses. We eat because we feel hunger, for instance.
Since our world is sin-cursed, human flesh knows good and evil. GOD is looking for those who love Him, trust Him, and want to follow Him, in spite of the flesh's weakness (our tendency towards evil because of our weakness). GOD knows our flesh is weak and He has made provisions for those who will try to be able to succeed in spite of this.
Thirdly, humans tend to trust our own wisdom, thinking, and judgment. Faith acknowledges that GOD knows what is best, infinitely more than we could discern. GOD is looking for children who will trust His love, provision, and wisdom.
These are just three—probably among many—reasons why GOD requires faith for someone to please Him.