There are at least four elements we should consider as a basis for our confidence in prayer.
We can be confident when we approach His throne because Christ our High Priest shed His blood for us and cleansed us inside and out; hence, on the basis of His blood we may come to Him courageously (or boldly), without fear, and with assurance that He will hear us and lovingly give us what we need.
A second basis for confidence is God’s Word. Through His Word we can know His will, and therefore, we are able to pray more directly and specifically, according to His will.
Thirdly, confidence is based on God’s character. Even if we had no definite promise from His Word, if we have some knowledge of His past mercies, and if we have grown to know His goodness, than we have a strong foundation for confidence in Him.
A forth foundation stone for confidence in prayer is God’s Spirit. We cannot have confidence in prayer without His Spirit; for it is the Sprit that urges us to believe and trust in Him. If we have The Holy Spirit we have every reason to be confident.