Sowing and reaping is a spiritual principle that is often misrepresented. God is not a cosmic ATM machine so you can always give $10 and get $100 in return. When we give we will be blessed. Sometimes the blessing may be in the form of wealth but not always. We don’t give in order to get. We give to bless others and to give glory to God.
When we return the tithe back to God He blesses the rest. When we give an offering over and above the tithe God will multiply it to bring the glory back to Him. When Jesus fed the multitudes He first blessed it and then directed the disciples to give it away. The miracle didn’t happen in the hands of the Master, the miracle happened in the hands of the disciples when they were obedient when they were obedient to give it away.