Worship is the only ministry which is directed to the Lord alone.
Prayer involves some worship, but also intercession for others and petitions for our own needs.
We minister unto the Lord by worshipping Him. We do not praise God to be heard by men. Also, keep in mind that since worship is a ministry unto the Lord, we should not worship God for the purpose of receiving material benefits or spiritual blessings from Him. It means to prostrate one's self, or to make one's self low. It also means to reverence and adore.