celo

One word covers both the abstract purpose and the physical thing you aim at, which is tidier than English managing it with goal, aim, purpose and target. The verb celi is transitive and means to aim at, so you celas ion with no preposition. Do not build clumsy scaffolding like por la celo de when a simple por plus an infinitive says it better: mi venis por helpi vin beats the version in the fifth example above for everyday use, and the noun version is what you want when the purpose itself is the topic.