It is important to know that sitting and the subsequent filling of church buildings with pews is a Protestant innovation. After the Protestant Reformation the focus of church service, for Protestants, moved from being worship orientated to lecture orientated, in the form of long sermons. Thus, the focus shifted from standing and worshiping to sitting and listening. Sadly, many Orthodox Churches are packed with pews, which present the Protestant ethos of observation rather than the Christian ethos of active participation in worship.
“In order to express to God our reverence before Him and our worship of Him, during prayer we stand, and do not sit; only the sick and elderly are allowed to pray sitting down.
Standing while at prayer is an ancient and God-ordained tradition. In Old Testament times, the congregation of Israel stood in the Temple (Neh. 9:4-5; 8:7, II Chron. 20:5,13), the Saints stand in heaven before the Throne of God (Is. 6:2; I Kings 22:19; Dan. 7:10; Rev. 7:11), and even Jesus Christ Himself said, When ye stand praying (Mk. 9:25). Therefore Christians, according to the apostolic teaching, stand through the Divine Services, where it is often proclaimed: 'Let us stand aright.'
In recognizing our sinfulness and unworthiness before God, and as a sign of our humility, we make bows during our prayers. There are bows from the waist, when we bow from the waist, and to the ground, when we bow down on our knees and touch our head to the ground (a prostration).” From The Law of God.