After a strong relationship with God, I have lost my spiritual zeal and my prayer life has grown cold. Whose fault is it?
When one of the disciples asked the Lord Jesus Christ to ".... teach us how to pray as John also taught his disciples" he expressed a universal spiritual need felt by us all. As you know, the Lord Jesus Christ taught the Lord's Prayer to His disciples. Holy Gospel of St. Matthew 6:9-13 is the version we pray in the Orthodox Divine Liturgy.
In Holy Gospel of St. Luke 11:8, the Lord Jesus Christ praises persistence. When we feel that our prayers have become void, long and cumbersome. Persistence comes in to assist us in keeping focused and in turning our attention toward God. When we need help we are to ask in prayer, seek through study, and knock through righteous living.
We should not allow ourselves to become weak. Quitting prayer is exactly what our enemy Satan wants us to do in order to launch his attacks. Praying daily the prayers within the Agpeya will encourage the spirit of prayer to abide in us.