By faith Abraham, when he was tested, offered up Isaac (Hebrews 11:17a NASB)
Sometimes it may seem impossible to do what God is telling you to do. You've considered every possible scenario and you just can't understand how it could possibly work.
You have to be able to trust in God and he will turn your obedience into pure joy and happiness. God uses our obedience to develop our faith. Sometimes we are told to do the impossible, we are told to do things that are downright scary sometimes, however once we take that first step God will show us what to do next. He uses our faith to teach us, but we can't learn until we take that initial leap of faith and obey.