Achan hide everything from men but he could not hide anything from God

The sin of one affects all and is the  responsibility of all 

Prayer is never a substitute for obedience.And we should God ever answer our prayer if we will not do what  He says?

Jashua 7:6 Then Joshua tore his clothes and fell to the earth on his face before the ark of the LORD until the evening, both he and the elders of Israel; and they put dust on their heads.

Jashua  22:20  Did not Achan the son of Zerah act unfaithfully in the things under the ban, and wrath fall on all the congregation of Israel? And that man did not perish alone in his iniquity.'"

No one lives to himself alone.Our actions always affect others for good or bad

Rom 14;7,13 For not one of us lives for himself, and not one dies for himself; Therefore let us not judge one another anymore, but rather determine this--not to put an obstacle or a stumbling block in a brother's way.

Achan's sin resulted in a humiliating defeat for the whole nation.

Jash 7;7-9 

Joshua said, "Alas, O Lord GOD, why did You ever bring this  people over the Jordan, only to deliver us into the hand  of the Amorites, to destroy us? If only we had been willing to dwell beyond the Jordan!

O Lord, what can I say since Israel has turned their back before their enemies?

For the Canaanites and all the inhabitants of the land will hear of it, and they will surround us and cut off our name from the earth. And what will You do for Your great name?"

"What will you do for your great name" we should always be more with God's reputation than with our own.

Jash  7:10-12

So the LORD said to Joshua, "Rise up! Why is it that you have fallen on your face?

Israel has sinned, and they have also transgressed My covenant which I commanded them. And they have even taken some of the things under the ban and have both stolen and deceived. Moreover, they have also put them among their own things

Therefore the sons of Israel cannot stand before their enemies; they turn their backs before their enemies, for they have become accursed. I will not be with you anymore unless you destroy the things under the ban from your midst.

The Lord rebukes Joshua, because it was not a time to pray, but to obey. 

Prayer is never a substitute for obedience.And we should God ever answer our prayer if we will not do what  He says?

"Accursed thing" -Achan was stealing from God.

''Used deception" -the sin deception or lying is often committed to cover up other sins.

Achan hide everything from men but he could not hide anything from God

Sin, if we do not judge it and put it away , will make us liable to "destruction", That is, God may abandon us to punishment for it.And sin may make it impossible for God to work with us.

Jash 8:2 If Achan had waited, he would have received his part in this plunder.

God gives us what He wants us to have in His own time(Matt 6:33)- if we trust and obey Him