Isaiah 55:6 (NIV) "Seek the Lord while He may be found, call upon Him while He is near."
It may sound as if God can't be found at times, or that sometimes He is afar off according to this scripture, however, God is omnipresent - He is everywhere at all times. David makes this statement in Psalms 139:7 (NIV) "Where can I go from Your Spirit? Or where can I flee from Your presence?" David fully understood that there was nowhere on earth that he could hide from God.
Isaiah is referring to the fact that there are times when we are more conscious of God than others. It is at those times that we need to reach out to Him, to pull upon His manifest presence while we are most aware of it. His presence being manifest among us is a work of grace in response to our hunger. God responds to His children hungering and thirsting after Him!
A. W. Tozer said, "The Presence and the manifestation of the Presence are not the same. There can be the one without the other. God is here when we are wholly unaware of it. He is manifest only when and as we are aware of His presence. On our part, there must be surrender to the Spirit of God, for His work is to show us the Father and the Son."
This can also explain why there may be times when one person 'feels' the presence of God while others in the same room seem oblivious to 'feeling' anything at all. It is the condition and the pursuit of one's heart that God responds to, He is a God to heart God. I believe that a person's pursuit and worship of God cannot be limited to certain methods nor certain outward expressions, likewise, when God's presence is felt, neither can a person's responses be contained nor limited to certain actions.
James 4:10 (NIV) "Humble yourselves before the Lord, and he will lift you up." This is the main ingredient for experiencing the presence of God, humbleness. Man cannot approach God in his pride and arrogance and expect God to bless it, we must come to God in humbleness and repentance, for we are mere flesh, and He is Almighty!
May we seek Him humbly and find Him!